Short packet optimization in WLAN systems

ABSTRACT

Mechanisms may be used for aggregating acknowledgement (ACK), block ACK (BA) and/or short packets transmissions for multi-user (MU) wireless communication systems. Aggregation mechanisms may be used for uplink (UL) and/or downlink (DL) orthogonal frequency division multiple access (OFDMA), and/or UL/DL multiple-user multiple input multiple output (MU-MIMO) transmissions, for example. Multi-user short packets may be aggregated and/or simultaneously transmitted for DL, UL, or peer-to-peer (P2P) transmissions.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/555,686, filed Sep. 5, 2017, which claims the benefit of U.S.National Stage, under 35 U.S.C. § 371, of International Application No.PCT/US2016/021216, filed Mar. 7, 2016, which claims the benefit of U.S.Provisional Application No. 62/129,561, filed Mar. 6, 2015, and U.S.Provisional Application No. 62/154,577, filed Apr. 29, 2015, thecontents of which are hereby incorporated by reference herein.

BACKGROUND

A wireless local area network (WLAN) in an Infrastructure Basic ServiceSet (BSS) mode may include an Access Point (AP) for the BSS and one ormore wireless transmit/receive units (WTRUs) (e.g., stations (STAs))associated with the AP. The AP may have access and/or an interface to aDistribution System (DS) or another type of wired and/or wirelessnetwork that may carry traffic in and out of the BSS. Traffic to WTRUsthat originates from outside the BSS may arrive through the AP and maybe delivered to the WTRUs. Traffic originating from WTRUs in the BSS andintended for destinations outside the BSS may be sent to the AP to bedelivered to the respective destinations. Traffic between WTRUs withinthe BSS may be sent through the AP where the source WTRU may sendtraffic to the AP and the AP may deliver the traffic to the destinationWTRU, for example. Such traffic between WTRUs within a BSS may bereferred to as peer-to-peer traffic. Such peer-to-peer traffic may besent directly between the source and destination WTRUs, for example witha direct link setup (DLS) using an Institute for Electrical andElectronic Engineers (IEEE) 802.11e DLS or an IEEE 802.11z tunneled DLS(TDLS). A WLAN using an Independent BSS (IBSS) mode may not include anAP, and may include WTRUs communicating directly with each other. Thismode of communication may be referred to as an “ad-hoc” mode ofcommunication.

SUMMARY

Mechanisms may be used for aggregating acknowledgement (ACK), block ACK(BA) and/or short packets transmissions for multi-user (MU) wirelesscommunication systems. Aggregation mechanisms may be used for uplink(UL) and/or downlink (DL) orthogonal frequency division multiple access(OFDMA), and/or UL/DL multiple-user multiple input multiple output(MU-MIMO) transmissions, for example. Multi-user short packets may beaggregated and/or simultaneously transmitted for DL, UL, or peer-to-peer(P2P) transmissions.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1A is a system diagram of an example communications system in whichone or more disclosed embodiments may be implemented;

FIG. 1B is a system diagram of an example wireless transmit/receive unit(WTRU) that may be used within the communications system illustrated inFIG. 1A;

FIG. 1C is a system diagram of an example radio access network and anexample core network that may be used within the communications systemillustrated in FIG. 1A;

FIG. 2 shows a frame format of an example multi-WTRU blockacknowledgment (ACK) (BA) frame;

FIG. 3 shows a frame format of another example multi-WTRU BA frame;

FIG. 4 shows a signaling diagram of an example scheduled channelprocedure for sequential ACKs/BAs for downlink (DL) orthogonal frequencydivision multiple access (OFDMA);

FIG. 5 shows a signaling diagram of another example scheduled channelprocedure for sequential ACKs/BAs for DL OFDMA;

FIG. 6 shows a signaling diagram of another example scheduled channelprocedure for sequential ACKs/BAs for DL OFDMA;

FIG. 7 shows a signaling diagram of another example scheduled channelprocedure for simultaneous ACKs/BAs for DL OFDMA over sub-channel(s);

FIG. 8 shows a frame format of an example code domain multiplexed UL ACKframe;

FIG. 9 shows a header format of an example grid-based time/frequencydomain approach for an UL ACK header;

FIG. 10 shows a header format of another example grid-basedtime/frequency domain approach for an UL ACK header;

FIG. 11 shows a header format of another example grid-basedtime/frequency domain approach for an UL ACK header;

FIG. 12 shows a signaling diagram of a simultaneous uplink (UL) ACKtransmission procedure using spatial orthogonal transmission;

FIG. 13 shows a block diagram of an example receiver structure at anaccess point (AP) using a spatial nulling scheme for UL ACK aggregation;

FIG. 14 shows a frame format of an example aggregation ACK request (AAR)control frame;

FIG. 15 shows a frame format of an example aggregated ACK (AA) responseframe;

FIG. 16 shows a frame format of an example block ACK (BA) AA responseframe;

FIG. 17 is a flow diagram of an example UL aggregated ACK responseprocedure;

FIG. 18 shows a signaling diagram of an example multi-user (MU) BAprocedure;

FIG. 19 shows a frame format of an example multi-dimensional (MD) MU BAframe;

FIG. 20 shows a frame format of an example null data packet (NDP) MU ACKbody field;

FIG. 21 shows a frame format of an example NDP MU BA header;

FIG. 22 shows a frame format of an example high-efficiency (HE)-SIG-Afield;

FIG. 23 shows a frame format of an example HE-SIG-B field;

FIG. 24 shows a frame format of an example DL ACK MU aggregation header;

FIG. 25 shows a frame format of an example MU BA control frame;

FIG. 26 shows a message diagram of an example MU aggregation procedure;

FIG. 27 shows a message diagram of another example MU aggregationprocedure;

FIG. 28 shows a message diagram of another example MU aggregationprocedure;

FIG. 29 shows a message diagram of an example MU aggregation procedurefor short packets with OFDMA and a narrow center channel; and

FIG. 30 shows a message diagram of another example MU aggregationprocedure.

DETAILED DESCRIPTION

FIG. 1A is a diagram of an example communications system 100 in whichone or more disclosed embodiments may be implemented. The communicationssystem 100 may be a multiple access system that provides content, suchas voice, data, video, messaging, broadcast, etc., to multiple wirelessusers. The communications system 100 may enable multiple wireless usersto access such content through the sharing of system resources,including wireless bandwidth. For example, the communications systems100 may employ one or more channel access methods, such as code divisionmultiple access (CDMA), time division multiple access (TDMA), frequencydivision multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrierFDMA (SC-FDMA), and the like.

As shown in FIG. 1A, the communications system 100 may include wirelesstransmit/receive units (WTRUs) 102 a, 102 b, 102 c, 102 d, a radioaccess network (RAN) 104, a core network 106, a public switchedtelephone network (PSTN) 108, the Internet 110, and other networks 112,though it will be appreciated that the disclosed embodiments contemplateany number of WTRUs, base stations, networks, and/or network elements.Each of the WTRUs 102 a, 102 b, 102 c, 102 d may be any type of deviceconfigured to operate and/or communicate in a wireless environment. Byway of example, the WTRUs 102 a, 102 b, 102 c, 102 d may be configuredto transmit and/or receive wireless signals and may include userequipment (UE), a mobile station, a fixed or mobile subscriber unit, apager, a cellular telephone, a personal digital assistant (PDA), asmartphone, a laptop, a netbook, a personal computer, a wireless sensor,consumer electronics, and the like.

The communications systems 100 may also include a base station 114 a anda base station 114 b. Each of the base stations 114 a, 114 b may be anytype of device configured to wirelessly interface with at least one ofthe WTRUs 102 a, 102 b, 102 c, 102 d to facilitate access to one or morecommunication networks, such as the core network 106, the Internet 110,and/or the other networks 112. By way of example, the base stations 114a, 114 b may be a base transceiver station (BTS), a Node-B, an eNode B,a Home Node B, a Home eNode B, a site controller, an access point (AP),a wireless router, and the like. While the base stations 114 a, 114 bare each depicted as a single element, it will be appreciated that thebase stations 114 a, 114 b may include any number of interconnected basestations and/or network elements.

The base station 114 a may be part of the RAN 104, which may alsoinclude other base stations and/or network elements (not shown), such asa base station controller (BSC), a radio network controller (RNC), relaynodes, etc. The base station 114 a and/or the base station 114 b may beconfigured to transmit and/or receive wireless signals within aparticular geographic region, which may be referred to as a cell (notshown). The cell may further be divided into cell sectors. For example,the cell associated with the base station 114 a may be divided intothree sectors. Thus, in one embodiment, the base station 114 a mayinclude three transceivers, i.e., one for each sector of the cell. Inanother embodiment, the base station 114 a may employ multiple-inputmultiple-output (MIMO) technology and, therefore, may utilize multipletransceivers for each sector of the cell.

The base stations 114 a, 114 b may communicate with one or more of theWTRUs 102 a, 102 b, 102 c, 102 d over an air interface 116, which may beany suitable wireless communication link (e.g., radio frequency (RF),microwave, infrared (IR), ultraviolet (UV), visible light, etc.). Theair interface 116 may be established using any suitable radio accesstechnology (RAT).

More specifically, as noted above, the communications system 100 may bea multiple access system and may employ one or more channel accessschemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 114 a in the RAN 104 and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Universal MobileTelecommunications System (UMTS) Terrestrial Radio Access (UTRA), whichmay establish the air interface 116 using wideband CDMA (WCDMA). WCDMAmay include communication protocols such as High-Speed Packet Access(HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed DownlinkPacket Access (HSDPA) and/or High-Speed Uplink Packet Access (HSUPA).

In another embodiment, the base station 114 a and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Evolved UMTSTerrestrial Radio Access (E-UTRA), which may establish the air interface116 using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A).

In other embodiments, the base station 114 a and the WTRUs 102 a, 102 b,102 c may implement radio technologies such as IEEE 802.16 (i.e.,Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000,CDMA2000 1×, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), InterimStandard 95 (IS-95), Interim Standard 856 (IS-856), Global System forMobile communications (GSM), Enhanced Data rates for GSM Evolution(EDGE), GSM EDGE (GERAN), and the like.

The base station 114 b in FIG. 1A may be a wireless router, Home Node B,Home eNode B, or access point, for example, and may utilize any suitableRAT for facilitating wireless connectivity in a localized area, such asa place of business, a home, a vehicle, a campus, and the like. In oneembodiment, the base station 114 b and the WTRUs 102 c, 102 d mayimplement a radio technology such as IEEE 802.11 to establish a wirelesslocal area network (WLAN). In another embodiment, the base station 114 band the WTRUs 102 c, 102 d may implement a radio technology such as IEEE802.15 to establish a wireless personal area network (WPAN). In yetanother embodiment, the base station 114 b and the WTRUs 102 c, 102 dmay utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE,LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG. 1A,the base station 114 b may have a direct connection to the Internet 110.Thus, the base station 114 b may not be required to access the Internet110 via the core network 106.

The RAN 104 may be in communication with the core network 106, which maybe any type of network configured to provide voice, data, applications,and/or voice over internet protocol (VoIP) services to one or more ofthe WTRUs 102 a, 102 b, 102 c, 102 d. For example, the core network 106may provide call control, billing services, mobile location-basedservices, pre-paid calling, Internet connectivity, video distribution,etc., and/or perform high-level security functions, such as userauthentication. Although not shown in FIG. 1A, it will be appreciatedthat the RAN 104 and/or the core network 106 may be in direct orindirect communication with other RANs that employ the same RAT as theRAN 104 or a different RAT. For example, in addition to being connectedto the RAN 104, which may be utilizing an E-UTRA radio technology, thecore network 106 may also be in communication with another RAN (notshown) employing a GSM radio technology.

The core network 106 may also serve as a gateway for the WTRUs 102 a,102 b, 102 c, 102 d to access the PSTN 108, the Internet 110, and/orother networks 112. The PSTN 108 may include circuit-switched telephonenetworks that provide plain old telephone service (POTS). The Internet110 may include a global system of interconnected computer networks anddevices that use common communication protocols, such as thetransmission control protocol (TCP), user datagram protocol (UDP) andthe internet protocol (IP) in the TCP/IP internet protocol suite. Thenetworks 112 may include wired or wireless communications networks ownedand/or operated by other service providers. For example, the networks112 may include another core network connected to one or more RANs,which may employ the same RAT as the RAN 104 or a different RAT.

Some or all of the WTRUs 102 a, 102 b, 102 c, 102 d in thecommunications system 100 may include multi-mode capabilities, i.e., theWTRUs 102 a, 102 b, 102 c, 102 d may include multiple transceivers forcommunicating with different wireless networks over different wirelesslinks. For example, the WTRU 102 c shown in FIG. 1A may be configured tocommunicate with the base station 114 a, which may employ acellular-based radio technology, and with the base station 114 b, whichmay employ an IEEE 802 radio technology.

FIG. 1B is a system diagram of an example WTRU 102. As shown in FIG. 1B,the WTRU 102 may include a processor 118, a transceiver 120, atransmit/receive element 122, a speaker/microphone 124, a keypad 126, adisplay/touchpad 128, non-removable memory 130, removable memory 132, apower source 134, a global positioning system (GPS) chipset 136, andother peripherals 138. It will be appreciated that the WTRU 102 mayinclude any sub-combination of the foregoing elements while remainingconsistent with an embodiment.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Array (FPGAs)circuits, any other type of integrated circuit (IC), a state machine,and the like. The processor 118 may perform signal coding, dataprocessing, power control, input/output processing, and/or any otherfunctionality that enables the WTRU 102 to operate in a wirelessenvironment. The processor 118 may be coupled to the transceiver 120,which may be coupled to the transmit/receive element 122. While FIG. 1Bdepicts the processor 118 and the transceiver 120 as separatecomponents, it will be appreciated that the processor 118 and thetransceiver 120 may be integrated together in an electronic package orchip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, thetransmit/receive element 122 may be an antenna configured to transmitand/or receive RF signals. In another embodiment, the transmit/receiveelement 122 may be an emitter/detector configured to transmit and/orreceive IR, UV, or visible light signals, for example. In yet anotherembodiment, the transmit/receive element 122 may be configured totransmit and receive both RF and light signals. It will be appreciatedthat the transmit/receive element 122 may be configured to transmitand/or receive any combination of wireless signals.

In addition, although the transmit/receive element 122 is depicted inFIG. 1B as a single element, the WTRU 102 may include any number oftransmit/receive elements 122. More specifically, the WTRU 102 mayemploy MIMO technology. Thus, in one embodiment, the WTRU 102 mayinclude two or more transmit/receive elements 122 (e.g., multipleantennas) for transmitting and receiving wireless signals over the airinterface 116.

The transceiver 120 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 122 and to demodulatethe signals that are received by the transmit/receive element 122. Asnoted above, the WTRU 102 may have multi-mode capabilities. Thus, thetransceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, forexample.

The processor 118 of the WTRU 102 may be coupled to, and may receiveuser input data from, the speaker/microphone 124, the keypad 126, and/orthe display/touchpad 128 (e.g., a liquid crystal display (LCD) displayunit or organic light-emitting diode (OLED) display unit). The processor118 may also output user data to the speaker/microphone 124, the keypad126, and/or the display/touchpad 128. In addition, the processor 118 mayaccess information from, and store data in, any type of suitable memory,such as the non-removable memory 130 and/or the removable memory 132.The non-removable memory 130 may include random-access memory (RAM),read-only memory (ROM), a hard disk, or any other type of memory storagedevice. The removable memory 132 may include a subscriber identitymodule (SIM) card, a memory stick, a secure digital (SD) memory card,and the like. In other embodiments, the processor 118 may accessinformation from, and store data in, memory that is not physicallylocated on the WTRU 102, such as on a server or a home computer (notshown).

The processor 118 may receive power from the power source 134, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 102. The power source 134 may be any suitabledevice for powering the WTRU 102. For example, the power source 134 mayinclude one or more dry cell batteries (e.g., nickel-cadmium (NiCd),nickel-zinc (NiZn), nickel metal hydride (NIMH), lithium-ion (Li-ion),etc.), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to the GPS chipset 136, which maybe configured to provide location information (e.g., longitude andlatitude) regarding the current location of the WTRU 102. In additionto, or in lieu of, the information from the GPS chipset 136, the WTRU102 may receive location information over the air interface 116 from abase station (e.g., base stations 114 a, 114 b) and/or determine itslocation based on the timing of the signals being received from two ormore nearby base stations. It will be appreciated that the WTRU 102 mayacquire location information by way of any suitablelocation-determination method while remaining consistent with anembodiment.

The processor 118 may further be coupled to other peripherals 138, whichmay include one or more software and/or hardware modules that provideadditional features, functionality and/or wired or wirelessconnectivity. For example, the peripherals 138 may include anaccelerometer, an e-compass, a satellite transceiver, a digital camera(for photographs or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, aBluetooth® module, a frequency modulated (FM) radio unit, a digitalmusic player, a media player, a video game player module, an Internetbrowser, and the like.

FIG. 1C is a system diagram of the RAN 104 and the core network 106according to an embodiment. As noted above, the RAN 104 may employ anE-UTRA radio technology to communicate with the WTRUs 102 a, 102 b, 102c over the air interface 116. The RAN 104 may also be in communicationwith the core network 106.

The RAN 104 may include eNode-Bs 140 a, 140 b, 140 c, though it will beappreciated that the RAN 104 may include any number of eNode-Bs whileremaining consistent with an embodiment. The eNode-Bs 140 a, 140 b, 140c may each include one or more transceivers for communicating with theWTRUs 102 a, 102 b, 102 c over the air interface 116. In one embodiment,the eNode-Bs 140 a, 140 b, 140 c may implement MIMO technology. Thus,the eNode-B 140 a, for example, may use multiple antennas to transmitwireless signals to, and receive wireless signals from, the WTRU 102 a.

Each of the eNode-Bs 140 a, 140 b, 140 c may be associated with aparticular cell (not shown) and may be configured to handle radioresource management decisions, handover decisions, scheduling of usersin the uplink and/or downlink, and the like. As shown in FIG. 1C, theeNode-Bs 140 a, 140 b, 140 c may communicate with one another over an X2interface.

The core network 106 shown in FIG. 1C may include a mobility managemententity gateway (MME) 142, a serving gateway 144, and a packet datanetwork (PDN) gateway 146. While each of the foregoing elements aredepicted as part of the core network 106, it will be appreciated thatany one of these elements may be owned and/or operated by an entityother than the core network operator.

The MME 142 may be connected to each of the eNode-Bs 140 a, 140 b, 140 cin the RAN 104 via an S1 interface and may serve as a control node. Forexample, the MME 142 may be responsible for authenticating users of theWTRUs 102 a, 102 b, 102 c, bearer activation/deactivation, selecting aparticular serving gateway during an initial attach of the WTRUs 102 a,102 b, 102 c, and the like. The MME 142 may also provide a control planefunction for switching between the RAN 104 and other RANs (not shown)that employ other radio technologies, such as GSM or WCDMA.

The serving gateway 144 may be connected to each of the eNode Bs 140 a,140 b, 140 c in the RAN 104 via the S1 interface. The serving gateway144 may generally route and forward user data packets to/from the WTRUs102 a, 102 b, 102 c. The serving gateway 144 may also perform otherfunctions, such as anchoring user planes during inter-eNode B handovers,triggering paging when downlink data is available for the WTRUs 102 a,102 b, 102 c, managing and storing contexts of the WTRUs 102 a, 102 b,102 c, and the like.

The serving gateway 144 may also be connected to the PDN gateway 146,which may provide the WTRUs 102 a, 102 b, 102 c with access topacket-switched networks, such as the Internet 110, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and IP-enableddevices.

The core network 106 may facilitate communications with other networks.For example, the core network 106 may provide the WTRUs 102 a, 102 b,102 c with access to circuit-switched networks, such as the PSTN 108, tofacilitate communications between the WTRUs 102 a, 102 b, 102 c andtraditional land-line communications devices. For example, the corenetwork 106 may include, or may communicate with, an IP gateway (e.g.,an IP multimedia subsystem (IMS) server) that serves as an interfacebetween the core network 106 and the PSTN 108. In addition, the corenetwork 106 may provide the WTRUs 102 a, 102 b, 102 c with access to thenetworks 112, which may include other wired or wireless networks thatare owned and/or operated by other service providers.

Other network 112 may further be connected to an IEEE 802.11 basedwireless local area network (WLAN) 160. The WLAN 160 may include anaccess router 165. The access router may contain gateway functionality.The access router 165 may be in communication with a plurality of accesspoints (APs) 170 a, 170 b. The communication between access router 165and APs 170 a, 170 b may be via wired Ethernet (IEEE 802.3 standards),or any type of wireless communication protocol. AP 170 a is in wirelesscommunication over an air interface with WTRU 102 d. In the following,WTRU, user, and station (STA) may be used interchangeably. Similarly,multi-user (MU), multi-WTRU and multi-STA may be used interchangeably.Additionally, channel(s), sub-channel(s), and resource unit(s) (RUs) maybe used interchangeably. Any of the mechanisms described herein may beused for acknowledgment (ACK) and/or block ACK (BA) and or negative ACK(NAK) elements or frames, control frames, and/or any type of short frameincluding short data and/or control frames.

A WLAN in an Infrastructure Basic Service Set (BSS) mode may include anAP for the BSS and one or more WTRUs (e.g., stations (STAs)) associatedwith the AP. The AP may have access or interface to a DistributionSystem (DS) or another type of wired and/or wireless network thatcarries traffic into and out of the BSS. In an example, using anInstitute of Electrical and Electronics Engineers (IEEE) 802.11acinfrastructure mode of operation, an AP may transmit a beacon on a fixedchannel, which may be the primary channel. This channel may be 20Megahertz (MHz) wide, and may be the operating channel of the BSS. Thischannel may be used by the WTRUs to establish a connection with the AP.The fundamental channel access mechanism in an IEEE 802.11 system may beCarrier Sense Multiple Access (CSMA) with Collision Avoidance (CSMA/CA).In a CSMA/CA mode of operation, every WTRU, including the AP, may sensethe primary channel. If a WTRU detects that the channel is busy, theWTRU may back off, such that only one WTRU may transmit at any giventime in a given BSS.

According to the IEEE 802.11n specification, High Throughput (HT) WTRUsmay use a 40 MHz wide channel for communication. This may be achieved,for example, by combining the primary 20 MHz channel with an adjacent 20MHz channel to form a 40 MHz wide contiguous channel.

According to the IEEE 802.11ac specification, Very High Throughput (VHT)WTRUs may support 20 MHz, 40 MHz, 80 MHz, and/or 160 MHz wide channels.For example, the 40 MHz and 80 MHz channels may be formed by combiningcontiguous 20 MHz channels similar to the IEEE 802.11n specificationdescribed above. A 160 MHz channel may be formed by combining eightcontiguous 20 MHz channels, or by combining two non-contiguous 80 MHzchannels, which may be referred to as an 80+80 configuration. For the80+80 configuration, the data, after channel encoding, may be passedthrough a segment parser that may divide the data into two streams.Inverse Fast Fourier Transform (IFFT) and time domain processing may bedone on each of the two streams separately. The streams may then bemapped on to the two channels, and the data may be transmitted. At thereceiver, this mechanism may be reversed, and the combined data may besent to the medium access control (MAC) layer.

Sub-1 GHz modes of operation may be supported by the IEEE 802.11af andIEEE 802.11ah specifications. For the IEEE 802.11af and IEEE 802.11ahspecifications, the channel operating bandwidths and/or carriers may bereduced relative to those used in IEEE 802.11n and IEEE 802.11ac, forexample. The IEEE 802.11af mode of operation may support 5 MHz, 10 MHzand/or 20 MHz bandwidths in the television (TV) White Space (TVWS)spectrum, and IEEE 802.11ah may support 1 MHz, 2 MHz, 4 MHz, 8 MHz,and/or 16 MHz bandwidths using non-TVWS spectrum. An example use casefor IEEE 802.11ah may be to support Meter Type Control (MTC) devices ina macro coverage area. MTC devices may have limited capabilitiesincluding support for limited bandwidths, and may be designed for a verylong battery life.

WLAN systems that support multiple channels and channel widths, such asIEEE 802.11n, IEEE 802.11ac, IEEE 802.11af, and IEEE 802.11ah, mayinclude a channel that is designated as the primary channel. In anexample, the primary channel may have a bandwidth equal to the largestcommon operating bandwidth supported by all WTRUs in the BSS. Thebandwidth of the primary channel may therefore be limited by thebandwidth supported by the WTRU in a BSS that supports the smallestbandwidth operating mode, for example.

For example, in an IEEE 802.11ah BSS, the primary channel may be 1 MHzwide if the BSS includes WTRUs (e.g., MTC type devices) that onlysupport a 1 MHz mode. This may be the case even if the AP and/or otherWTRUs in the BSS support 2 MHz, 4 MHz, 8 MHz, 16 MHz, or greater channelbandwidth operating modes. Carrier sensing and/or network allocationvector (NAV) settings may depend on the status of the primary channel.For example, if the primary channel is busy, for example when a WTRUsupporting only a 1 MHz operating mode is transmitting to the AP, thenthe entire available frequency bands may be considered busy even thoughmajority of the available frequency remains idle.

In the United States, the available frequency bands which may be used byIEEE 802.11ah may include 902 MHz to 928 MHz. In Korea, the availablefrequency bands which may be used by IEEE 802.11ah may include 917.5 MHzto 923.5 MHz. In Japan, the available frequency bands which may be usedby IEEE 802.11ah may include 916.5 MHz to 927.5 MHz. In these cases, thetotal bandwidth available for IEEE 802.11ah may include a bandwidth from6 MHz to 26 MHz depending on the country code.

To improve spectral efficiency, IEEE 802.11ac may include the concept ofdownlink Multi-User MIMO (MU-MIMO) transmission to multiple WTRUs in thesame symbol's time frame (e.g., during a downlink OFDM symbol). Thepotential use of downlink MU-MIMO is also being considered for IEEE802.11ah. In some cases, interference of waveform transmissions tomultiple WTRUs may not present a problem for an IEEE 802.11ac BSSbecause downlink MU-MIMO may use the same symbol timing to multipleWTRUs. However, because some or all WTRUs involved in MU-MIMOtransmission with the AP may need to use the same channel or band, theoperating bandwidth may be limited to the smallest channel bandwidththat is supported by the WTRUs which are included in the MU-MIMOtransmission with the AP.

WLAN systems may use of acknowledgement and/or short packet aggregationmechanisms. Wireless transmissions may be unreliable even thoughprotection mechanisms such as channel coding and interleaving may beused to protect the transmissions. Therefore, mechanisms for theacknowledgement of correct packet reception may be used in WLAN systems.A WTRU/AP that successfully receives a data frame addressed to it maysend a positive acknowledgement, known as an ACK, to the sender. If aWTRU/AP transmitting a frame does not receive an ACK within a prescribedamount of time, it may assume that the data frame was not receivedcorrectly and may retransmit it. However, not all data frames may or canbe acknowledged in this way. The IEEE 802.11 standard may also support a“No ACK” mode where the originator or sender of a data frame mayindicate that no acknowledgement (i.e. ACK) is expected from therecipient of the data frame.

Block acknowledgement (BA) is used, for example, in IEEE 802.11e. BA mayimprove system efficiency by allowing the recipient of multiple framesto transmit a single block ACK to acknowledge a block of data frames.This may reduce overhead since the preambles and headers may only besent once. Examples of BA approaches include, but are not limited to:Immediate Block ACK and Delayed Block ACK. A short ACK packet format isproposed IEEE 802.11ah that includes only short training fields (STF),long training fields (LTF), and signal fields (SIG).

WLAN systems may use short packet aggregation mechanism. The IEEE 802.11standards may use single-user (SU) aggregation mechanisms such asaggregated medium access control protocol data unit (AMPDU) andaggregated medium access control service data unit (AMSDU). The IEEE802.11ac specification includes Downlink (DL) multi-user (MU)multiple-input-multiple-output (MU-MIMO) as a MU aggregation method,such that polled ACKs may be sent individually in the uplink (UL). Thisapproach to DL MU-MIMO may add overhead, especially for shorter packets.

The IEEE 802.11 High Efficiency WLAN (HEW) Study Group (SG) was createdto explore the scope and purpose of enhancing the quality of service allusers experience for a broad spectrum of wireless users in many usagescenarios including high-density scenarios in the 2.4 GHz and 5 GHzband. The HEW SG is considering new use cases that support densedeployments of APs, WTRUs, and/or associated Radio Resource Management(RRM) technologies. Potential applications for HEW include, but are notlimited to: emerging usage scenarios such as data delivery for stadiumevents; high user density scenarios such as train stations orenterprise/retail environments; evidence for an increased dependence onvideo delivery; and wireless services for medical applications.

The IEEE Standards board approved a Task Group (TG) for IEEE 802.11axbased on a Project Authorization Request (PAR) and Criteria forStandards Development (CSD) developed in the HEW SG. Via the IEEE802.11ax Task Group (TGax), it has been determined that measured trafficfor a variety of applications, including network applications, may havea high likelihood of including short packets. For example, suchapplications may include, but are not limited to: virtual office;transmission power control (TPC) ACK; video streaming ACK;device/controller (e.g., mouse, keyboard, and/or game controller);access including probe request and/or response; network selectionincluding probe requests, and/or access network query protocol (ANQP);and/or network management control frames.

IEEE 802.11ax may have MU features that may include UL and/or DL OFDMA,and/or UL and/or DL MU-MIMO. Accordingly, mechanisms described hereinmay be used for multiplexing DL acknowledgments (ACKs) sent in responseto UL MU transmissions. IEEE 802.11 standards may include a largeoverhead and/or delay for short packet(s) and/or payload(s), and thussolutions described herein may be used to achieve any of the followinggoals: enhance MAC efficiency; reduce medium access overhead and/ordelay for short packets/bursts; provide effective ACK and otherpotential feedback information aggregation schemes for MU featuresincluding DL and UL OFDMA and MU-MIMO; and/or provide effectivetechniques that allow for simultaneous MU short packet transmissions.

A framework may be provided for IEEE 802.11ax for multi-WTRU (e.g.,multi-STA) BA control frame to acknowledge multiple WTRUs after UL MUtransmission.

FIG. 2 shows a frame format of an example multi-WTRU BA frame 200. Themulti-WTRU BA frame 200 may be defined by modifying a multi-trafficidentifier (multi-TID) BA frame format, for example. The multi-WTRU BAframe 300 may include a MAC header 202. The multi-WTRU BA frame 200 mayinclude, but is not limited to include, any of the following fields: aframe control field 204 (e.g., 2 octets); a duration and/oridentification (ID) field 206 (e.g., 2 octets); a receiving WTRU address(RA) field 208 (e.g., 6 octets); a transmitting WTRU address (TA) field210 (e.g., 6 octets); a BA control field 212 (e.g., 2 octets); a BAinformation field 214 (e.g., variable length); and/or a frame checksequence (FCS) 216 (e.g., 4 octets). The BA control field 212 mayindicate that the frame 200 is a multi-WTRU BA frame. In an example, theBA control field 212 may include 16 bits, B0 to B15. The BA controlfield 212 may include, but is not limited to include, any of thefollowing subfields: a block acknowledgment request (BAR) ACK policyfield 218 (e.g., bit B0); a multi-TID field 220 (e.g., bit B1); acompressed bitmap field 222 (e.g., bit B2); a group code recording (GCR)field 224 (e.g., bit B3); reserved field(s) 226 (e.g., bits B4 to B11);and/or a TID_INFO field 228 (e.g., bits B12-B15).

The BA information field 214 may include information that is repeatedfor each TID. The repeated information in the BA information field 214may include, but is not limited to include, any of the following: aper-TID information field 230 (e.g., 2 octets); a BA starting sequencecontrol field 232 (e.g., 2 octets); and/or a BA bitmap field 234 (e.g.,8 octets). Each repeated information for each TID within the BAInformation field 214 may be addressed to different WTRU(s). Forexample, bits B0-B10 of the per-TID information field 230, which may bepart of a reserved field 236 (e.g., bits B0-B11), may carry anassociation identifier (AID) field identifying the intended receiver ofthe BA Information field 214. The per-TID information field 230 mayinclude a TID value field 238 (e.g bits B12 to B16).

FIG. 3 shows a frame format of another example multi-WTRU BA frame 300.The multi-WTRU BA frame 300 may be defined by modifying a multi-TID BAframe format, for example. The multi-WTRU BA frame 300 may include a MACheader 302. The multi-WTRU BA frame 300 may include, but is not limitedto include, any of the following fields: a frame control field 304(e.g., 2 octets); a duration and/or ID field 306 (e.g., 2 octets); an RAfield 308 (e.g., 6 octets); a TA field 310 (e.g., 6 octets); a BAcontrol field 312 (e.g., 2 octets); a BA information field 314 (e.g.,variable length); and/or an FCS 316 (e.g., 4 octets). The BA controlfield 312 may indicate that the frame 300 is a multi-WTRU BA frame. Inan example, the BA control field 312 may include 16 bits, B0 to B15. TheBA control field 312 may include, but is not limited to include, any ofthe following subfields: a BAR ACK policy field 318 (e.g., bit B0); amulti-TID field 320 (e.g., bit B1); a compressed bitmap field 322 (e.g.,bit B2); a GCR field 324 (e.g bit B3); reserved field(s) 326 (e.g., bitsB4 to B11); and/or a TID_INFO field 328 (e.g., bits B12-B15).

The BA information field 314 may include information that is repeatedfor each TID. The repeated information in the BA information field 314may include, but is not limited to include, any of the following: aper-TID information field 330 (e.g., 2 octets); a BA starting sequencecontrol field 332 (e.g., 2 octets); and/or a BA bitmap field 334 (e.g.,8 octets). The multi-WTRU BA frame 300 may allow an ACK indication perWTRU, in addition to or instead of a BA. In a BA information field 314,if bit B11 in the per-TID info field 330 is set, then the BA bitmapsubfield 334 and/or the BA starting sequence control (SC) subfield 332may not be present in the BA information field 314. In this scenario,the BA information field 314 may indicate an ACK for the WTRU in B11 ofthe per-TID info field 330 with AID indicated in bits B0 to B10 in theper-TID info field 330. Bits B0-B10 of the per-TID information field 330may carry an AID field identifying the intended receiver of the BAinformation field 314. The per-TID information field 330 may include aTID value field 338 (e.g bits B12 to B16).

UL ACK aggregation for DL OFDMA and/or DL MU-MIMO may be used in WLANsystems. A Polled-ACK mechanism, used in IEEE 802.11ac for DL MU MIMOfor example, may be used for DL OFDMA for backwards compatibility.However, a polled-ACK mechanism may not be efficient for DL MUtechnologies as it may create excessive overhead by sending ACKsindividually in the UL. Therefore, more efficient mechanisms andprocedures may be designed and used for DL OFDMA and/or DL MU-MIMO.

ACK/BA aggregation in the DL direction may not be available in the IEEE802.11 specifications. For UL MU features in IEEE 802.11 systems, thatmay include UL OFDMA and/or UL MU-MIMO, mechanisms may be used formultiplexing DL acknowledgments (ACKs) sent in response to UL MUtransmissions.

The Multi-WTRU BA control frame formats described in FIGS. 2 and 3 forDL MU BA/ACK aggregation may, or may not, be affected by any of thefollowing considerations: the RA field may not be easily interpreted asa receiver MAC address because multiple receivers (e.g., multipleWTRUs/STAs) may be included in the frame transmission; the BAinformation subfield length of the BA frame format may be obtained fromthe TID_INFO subfield in the BA Control field, although the frame formatmay not allow it; The 9 or 10 bits partial AID in the per-TID info fieldmay cause confusion at the receiver (e.g., WTRU) due to the limited bitlength; the length of BA information may be variable since both ACK andBA may be supported, such that a receiver (e.g., WTRU) may be requiredto decode the entire information in order to obtain the ACK/BA foritself; an indication may be needed to indicate that the frame is amulti-WTRU BA; a multi-TID BAR and/or multi-TID BA may be needed forHT-immediate operation; and/or a BAR/BA protocol may need to beredefined for Multi-WTRU BA.

Short data packets may use MU aggregation in the UL, DL and/orpeer-to-peer transmissions in WLAN systems, such as in IEEE 802.11axnetworks for example. Measured traffic for a variety of applications,including network applications, may have a high likelihood of includingshort packets, and certain network applications may also generate shortpackets. The IEEE 802.11n and 802.11ac specifications may include AMPDUsfor single user (SU) aggregation within the same burst, and MUaggregation mechanisms may or may not be used in IEEE 802.11specifications. In IEEE 802.11 specifications, small packets may facesimilar amounts of overhead and/or delay as larger packets. Thus, MACand physical (PHY) layer procedures with parallel transmissions of smallpackets in code/spatial/frequency/time domain(s) and/or effectivemechanisms for simultaneous MU short packet transmission may be used inorder to enhance MAC efficiency and reduce medium access overhead and/ordelay for short packets.

Similarly, ACK and/or short data packets may be aggregated in DL, UL,and/or peer-to-peer transmissions in WLAN systems (e.g., IEEE 802.11axnetworks). Because MU features, including OFDMA and MU-MIMO, may be usedfor both UL and DL, mechanisms and processes may be used to aggregatecontrol frames, such as ACK and/or short data packets, which in order toenhance MAC efficiency and reduce medium access overhead and/or delayfor short packets/bursts and MU features.

IEEE 802.11 MAC designs may be optimized for packet transmissions overlarge bandwidths. Short packet optimization mechanisms may optimize thereservation of wide channel bandwidths. For example, in IEEE 802.11ac aprocedure for reserving bandwidths that are larger than 20 MHz mayenhance the use of CTS/RTS frame exchanges to allow a backwardcompatible reservation of 40 MHz and/or 80 MHz channel bandwidths. IEEE802.11ac optimizations for small packet transmissions may be used formanagement frames, such that optimizations for small data packets may belimited.

Example approaches for UL ACK aggregation may include, but are notlimited to, any of the following: UL scheduled ACK aggregation; UL ACKaggregation in code domain; UL ACK aggregation in the spatial domain;and/or UL ACK aggregation for DL OFDMA and/or MU-MIMO. These exampleapproaches are discussed in detail below.

According to an example approach, UL scheduled ACK aggregation may beused to reduce overhead and/or delay for DL OFDMA and/or DL-MIMOtransmissions. A procedure at an AP may identify WTRUs that are intendedfor a scheduled response to the AP in order for a group of WTRUs tocommunicate with their associated AP. Similarly, a WTRU procedure may beused for enabling the scheduled response. Example methods for enabling ascheduled response of an ACK and/or block ACK (BA) from multiple WTRUsto the AP as part of MU ACK aggregation are described herein.

In an example method, for responding to DL OFDMA, and/or DL MU-MIMO datatransmission to a group of WTRUs, a control frame may be used toschedule or signal the response procedure for the group of sequential orsimultaneous ACKs and/or BAs for UL MU ACK aggregation. For example, thecontrol frame may be sent in an interval of time equal to x shortinter-frame spacing (xSIFS) after DL MU data transmission, where x maybe 1 or any positive integer.

In another example method, control information may be used to signal theresponse procedure for a group of scheduled ACKs and/or BAs for UL MUACK aggregation. For example, the control information may be included bythe AP in a DL frame header explicitly and/or implicitly. As an exampleof explicit control information, the control information indicatinggroup ordering of UL MU ACK aggregation may be included in the DL MUdata frame physical layer convergence protocol (PLCP) header transmittedover the entire channel and/or may be included in each dedicatedWTRU-specific sub-channel PLCP header. As an example of implicit controlinformation, it may be defined that once the WTRUs have received a DL MUdata frame, the corresponding MU ACKs and/or BAs are aggregated andsequentially transmitted as a group in the UL.

In another example method, a management frame may be used to schedule DLMU data transmissions and/or UL MU ACK/BA transmissions. The managementframe may be sent in the DL by the AP to carry the schedulinginformation for subsequent DL and UL transmissions.

The control or management frame may include, but is not limited toinclude, any of the following information: the number of WTRUs scheduledto feedback the acknowledgement; which group of WTRUs and/or which WTRUsare scheduled to feedback the acknowledgement; by which resource unitthe scheduled ACKs and/or BAs for each WTRU should feedback to the AP;whether the ACKs and/or BAs are allowed to be aggregated with otherpackets such as data and/or control frames; and/or any other schedulinginformation such as BAR control and/or BAR information for eachscheduled WTRU.

In an example scenario, if a WTRU does not detect or successfullydemodulate the control or management frame (and thus misses its ULACK/BA transmission), the AP may detect this within a certain period oftime (e.g., point coordination function (PCF) inter-frame spacing(PIFS)) after the control or management frame transmission. If the UL MUACK/BA transmission time is too long, the AP may resend a recoverycontrol or management frame with a new schedule for the other WTRUs thatdid not successfully feedback their UL ACKs/BAs. For example, the AP mayresend the recovery control or management frame a period of PIFs afterthe previous control or management frame.

According to an example, WTRUs in a group may respond to a message forthe scheduled ACKs and/or BAs as described in one or a combination ofthe example methods. For example, a group of WTRUS may respond in aninterval of time equal to ySIFS, where y may be any positive integergreater than or equal to 1. WTRUs within the group may respond usingACKs and/or BAs sequentially with or without z short inter-frame space(zSIFS), or z reduced inter-frame space (zRIFS), where z may be anypositive integer greater than or equal to 1. In a scenario where SIFS orRIFS is not used, the MU ACKs and/or BAs may share the same preambleand/or header.

FIG. 4 shows a signaling diagram of an example scheduled channelprocedure 400 for sequential ACKs/BAs for DL OFDMA. In the examplescenario of FIG. 4, WTRUs 401-404 may be in communication with AP 405.AP 405 may transmit data PLCP protocol data units (PPDUs) 406, 408, 410and 412 to WTRUs 401, 402, 403, and 404, respectively. The data PPDUs406, 408, 410 and 412 may be transmitted in parallel over differentchannel(s), sub-channel(s) or resource units (RUs) in DL OFDMA, forexample. Using OFDMA, which is a multi-user variant of the OFDM scheme,multiple-access may be achieved by assigning subsets of subcarriers todifferent users, allowing simultaneous data transmission by severalusers. In OFDMA, the resources may be allocated in two dimensionalregions over time and frequency. In FIG. 4, the time region may coverthe entire data portion of the MU PPDU 430 (including data PPDUs 406,408, 410, and 412), and in frequency domain, the subcarriers may bedivided into several groups of subcarriers where each group may bedenoted as a resource unit (RU) or sub-channel that may be allocated fordata transmission 406, 408, 410, and 412 to each of the users (WTRUs401, 402, 403 and 404). The simultaneous data PPDU transmissions 406,408, 410, and 412 in an MU PPDU 430 in DL OFDMA and/or DL MU MIMO mayend at the same time.

The transmission of data PPDUs 406, 408, 410 and 412 may be followed byan interframe spacing xSIFs 414. The AP 405 may send a control frame 416to the WTRUs 401-404 to schedule or indicate the group of WTRUs (e.g.,WTRUs 401-404) that are identified for sequential transmission of ACKsand/or BAs to the AP 405. The control frame 416 may use the entirechannel bandwidth, for example. The use of control frame 416 may incurless overhead and/or delay than using a polled ACK approach. Each ACKand/or BA 420, 422, 424, and 426 may be sent sequentially over theentire channel bandwidth to the respective WTRUs 401, 402, 403, and 404,within the group.

FIG. 5 shows a signaling diagram of another example scheduled channelprocedure 500 for sequential ACKs/BAs for DL OFDMA. In the examplescenario of FIG. 5, WTRUs 501-504 may be in communication with AP 505.AP 405 may transmit data PPDUs 506, 508, 510 and 512 to WTRUs 501, 502,503, and 504, respectively. The data PPDUs 506, 508, 510 and 512 may betransmitted in parallel over different channel(s) or sub-channel(s) andmay be part of MU PPDU 530, for example. The transmission of data PPDUs506, 508, 510 and 512 may be followed by an interframe spacing xSIFs514.

The AP 505 may send a control frame 516 to the WTRUs 501-504 to scheduleor indicate the group of WTRUs (e.g., WTRUs 501-504) that are identifiedfor sequential transmission of ACKs and/or BAs to the AP 505. Thecontrol frame 516 may use the entire channel bandwidth, for example.Each ACK and/or BA 520, 522, 524, and 526 may be sent sequentially overthe entire channel bandwidth to the respective WTRUs 501, 502, 503, and504, within the group. The transmission of the ACK and/or BA 520, 522,524, and 526 may be separated by ySIFs 518 and/or zSIFS 521, 523 and/or525, for example.

FIG. 6 shows a signaling diagram of another example scheduled channelprocedure 600 for sequential ACKs/BAs for DL OFDMA. In the examplescenario of FIG. 6, WTRUs 601-604 may be in communication with AP 605.AP 605 may transmit data PPDUs 606, 608, 610 and 612 to WTRUs 601, 602,603, and 604, respectively. The data PPDUs 606, 608, 610 and 612 may betransmitted in parallel over different channel(s) or sub-channel(s) andmay be part of MU PPDU 630, for example. The transmission of data PPDUs606, 608, 610 and 612 may be followed by an interframe spacing xSIFs614.

The AP 605 may send a control frame 616 to the WTRUs 601-604 to scheduleor indicate the group of WTRUs (e.g., WTRUs 601-604) that are identifiedfor sequential transmission of ACKs and/or BAs to the AP 605. Thecontrol frame 616 may use the entire channel bandwidth, for example.Each ACK and/or BA 620, 622, 624, and 626 may be sent sequentially overthe entire channel bandwidth to the respective WTRUs 601, 602, 603, and604, within the group. The transmission of the ACK and/or BA 620, 622,624, and 626 may be separated by ySIFs 618 and/or zRIFS 621, 623 and/or625, for example. The use of RIFS may reduce the MAC overhead as much asare more than using SIFS.

FIG. 7 shows a signaling diagram of another example scheduled channelprocedure 700 for simultaneous ACKs/BAs for DL OFDMA oversub-channel(s). In the example scenario of FIG. 7, WTRUs 701-704 may bein communication with AP 705. AP 705 may transmit data PPDUs 706, 708,710 and 712 to WTRUs 701, 702, 703, and 704, respectively. The dataPPDUs 706, 708, 710 and 712 may be transmitted in parallel overdifferent channel(s) or sub-channel(s), and may be part of MU PPDU 730for example. The transmission of data PPDUs 706, 708, 710 and 712 may befollowed by an interframe spacing xSIFs 714.

The AP 705 may send a control frame 716 to the WTRUs 701-704 to scheduleor indicate the group of WTRUs (e.g., WTRUs 701-704) that are identifiedfor (simultaneous) transmission of MU ACKs and/or BAs to the AP 705. Thecontrol frame 716 may use the entire channel bandwidth, for example. Thecontrol frame 716 may be followed by a ySIFS 714.

As indicated by the control frame 716, the MU ACKs (and/or BAs) 720,722, 724 and 726 may be simultaneously transmitted from the respectiveWTRUs 701, 702, 703, and 704 on one or more correspondingsub-channel(s). Scheduled sub-channel based ACKs or BAs, such as MU ACKs(or BAs) 720, 722, 724 and 726, may involve an UL OFDMA capability. TheMU ACKs (and/or BAs) 720, 722, 724 and 726 may be equivalentlysupplemented and/or replaced by orthogonal spatial domain transmissionof MU ACKs and/or BAs.

Example mechanisms for CDMA UL ACK aggregation, including UL ACKaggregation in the code domain, are described herein and may be used forDL OFDMA and/or DL MU-MIMO. Such mechanisms may facilitate a tradeoffbetween feedback overhead, and UL ACK/control frame aggregationefficiency. For the mechanisms described herein, UL ACK aggregation mayapply to UL ACK, UL control frame and/or short (data and/or control)frame aggregation.

In an example, a grid-based time and frequency domain solution may beused for UL ACK MU aggregation. MU ACKs and/or BAs may be simultaneouslysent on the same time and frequency grid by using code domain codes orsequences. Because DL OFDMA and/or DL MU-MIMO may be used, up to sixteensimultaneous UL ACKs may be used to support four downlink streams onfour downlink sub-channels, for example.

In an example, an UL MU ACK channel may be divided into one, two, orfour uplink sub-channels where the sub-channels may be uniquely definedfor the UL ACK, or associated UL management frame channel. For example,in the case that an UL channel bandwidth is 20 MHz (e.g., in IEEE802.11ac), the one, two, or four UL sub-channels may each have abandwidth of 20, 10, or 5 MHz, respectively, using a 256 point FFT forthe 20 MHz channel. Other combinations of sub-channel(s) andbandwidth(s) may be used. OFDMA UL channel configurations may support upto four simultaneous UL ACKs in a 20 MHz channel, for example.

The complexity of a spreading code approach may increase linearly withbandwidth, while the complexity of an OFDM approach may increaselogarithmically with bandwidth. Thus, a spreading code approach may beimplemented over a smaller bandwidth than the maximum channel bandwidthof the data channel in WLAN to reduce complexity. Furthermore, aspreading code may be applied to each of the UL ACK sub-channelsdiscussed above (e.g., the sub-channels used for the MU ACKs and/or BAs720, 722, 724, and 726 in FIG. 7). For example, up to four orthogonalspreading codes may be defined for four UL 5 MHz sub-channels (orchannels), where each spreading code may represent an ACK for one of upto sixteen WTRUs in an UL OFDMA channel. The four UL 5 MHz sub-channels,each with up to four spreading codes, may be defined as a controlsub-frame that may occur prior to the data sub-frame(s). The subsequentdata sub-frame(s) may have a bandwidth that is greater than thebandwidth of the ACK (or control frame) sub-channels (e.g., 20 MHz>5MHz).

In the examples of FIGS. 8-10, it may be assumed that there are foursub-channels (but it may apply to any number of sub-channels).

FIG. 8 shows a frame format of an example code domain multiplexed UL ACKframe 800. UL ACK frame 800 may include, but is not limited to include,any of the following: STF/LTF/SIG fields 802 ₁ . . . 802 ₄ according toan IEEE 802.11 specification such as IEEE 802.11ah, for example;STF/LTF/SIG fields 804 ₁ . . . 804 ₄ in accordance with the IEEE802.11ax specification; code domain multiplexed ACK fields 806 ₁ . . .806 ₄; and/or data field 810. Each ACK field 806 ₁ . . . 806 ₄ mayinclude, for example, four multiplexed UL ACKs (or control/short frames)ACK₁ . . . ACK₄ that may be spread and multiplexed using four spreadingcodes C₁ . . . C₄ and may correspond to the four sub-channels.

FIG. 9 shows a header format of an example grid-based time/frequencydomain approach for an UL ACK header 900. The UL ACK header 900 mayinclude, but is not limited to include, any of the following: STF fields902 ₁ . . . 902 ₄ that may cover the entire frequency band or channelbandwidth; LTF fields 904 ₁ . . . 904 ₄, where LTF 904 ₁ may coversub-channel 1, LTF 9042 may cover sub-channel 2, and so on, fordifferent WTRUs; SIG fields 906 ₁ . . . 906 ₄; and/or ACK fields 908 ₁ .. . 908 ₄ that may serve as acknowledgements for sub-channels 1-4. TheSTF 902 ₁ . . . 902 ₄ may be duplicated (i.e. identical) in eachsub-channel, for example.

FIG. 10 shows a header format of another example grid-basedtime/frequency domain approach for an UL ACK header 1000. The UL ACKheader 1000 may include, but is not limited to include, any of thefollowing: STF field 1002 that may be sent over the entire (whole)channel bandwidth; LTF fields 1004 ₁ . . . 1004 ₄, where LTF 1004 ₁ maycover sub-channel 1, LTF 1004 ₂ may cover sub-channel 2, and so on, fordifferent WTRUs; SIG fields 1006 ₁ . . . 1006 ₄ for sub-channels 1-4;and/or ACK fields 1008 ₁ . . . 1008 ₄ that may serve as acknowledgementsfor sub-channels 1-4.

FIG. 11 shows a header format of another example grid-basedtime/frequency domain approach for an UL ACK header 1100. The UL ACKheader 1100 may include, but is not limited to include, any of thefollowing: STF field 1102 that may be sent over the entire (whole)channel bandwidth; LTF field 1104 that may be sent over the entirechannel bandwidth; SIG fields 1106 ₁ . . . 1106 ₄ for sub-channels 1-4;and/or ACK fields 1108 ₁ . . . 1108 ₄ that may serve as acknowledgementsfor sub-channels 1-4. In the example of FIG. 11, LTF 1104 may be sent onthe whole channel, but each WTRU may only use the LTF allocated to thecorresponding sub-channel to do channel estimation for the associatedsub-channel. In addition to the above examples, a combination of thecode domain and time domain may be used for UL ACK aggregation, whichmay facilitate a robust error recovery capability.

According to an example, CDMA codes or sequences may be used MU ACKaggregation. For example, any one or any combination of the followingcodes may be used for MU ACK aggregation: Zadoff-Chu code; orthogonalvariable spreading factor (OVSF) code; short/long scrambling codes;variable spreading and chip repetition factor (CDMA coding); spreadorthogonal frequency division multiplexing (OFDM) and/or coded-OFDM(COFDM) coding; fast/slow frequency spread/hopping code; Hadamard code;and/or other orthogonal codes. In another example, CDMA codes may bedesigned for MU ACK aggregation that provide orthogonality and asufficient number codes in the frequency and/or time domain.

Procedures for signaling CDMA codes or sequences to WTRUs for MU ACKaggregation are described herein. CDMA codes or sequences may besignaled to WTRUs in various ways for MU ACK aggregation. For example,CDMA codes or sequences may be signaled or assigned by a beacon orprobe. For example, a mother code for MU ACK aggregation may be signaledin the beacon, and the remaining WTRU-specific code(s) may be signaledin the PLCP and/or MAC header for the corresponding WTRU, or implicitlysignaled by the sub-channel where the WTRU transmits the data frame. Inanother example, CDMA codes or sequences may be signaled or assigned byusing probe request and response for code exchange, such that the probeframe may be modified such that it is suitable for a CDMA-basedsolution.

In another example, OVSF or OVSF-like tree based CDMA codes may be usedsimultaneously for MU transmission or MU ACK aggregation in the codedomain. A number of codes may be based on the number of WTRUs to besimultaneously transmitted by CDMA codes. For example, K WTRUs may needK CDMA codes to support simultaneous transmission, so that the spreadfactor (SF) may be selected equal to or bigger than K. In order tomaintain the orthogonality of OVSF codes, certain rules may be appliedin the selection of the OVSF codes for MU ACK aggregation andtransmission. For example, an OVSF code may be selected to prevent useof a code that is on an underlying branch with higher spreading factor(SF). Similarly, a smaller SF code on the path to the root of the treemay be prevented from being used.

An OVSF code as described above may be signaled to a WTRU using, but notlimited to, any one or any combination of the following approaches:signaling the OVSF code in a control frame, PLCP header of the WTRU,and/or MAC header of the WTRU, for example; explicitly signaling the SFand the OVSF code index within the tree with SF=K using a managementframe, such as a beacon, probe signal, and/or a control frame; and/orexplicitly signaling the selected SF and implicitly signaling the OVSFcode index by a pre-defined order, such as an ascending or descendingorder, within the SF code group for MU transmission or MU ACKaggregation.

According to an example, ACKs received at the AP from multiple WTRUs maybe synchronized, as described herein. If propagation delays and/orprocessing delays from different WTRUs are within a cyclic prefix, areceiver may be able to decode signals from the different WTRUs.However, where the cyclic prefix is not able to cover the difference indelays from different WTRUs, time synchronization may be used in orderto maintain spatial orthogonality or orthogonality in the code/sequencedomain among the signals. Once signals from multiple transmitters are inover the air and combined together, it may be difficult to change eachsignal individually. Unless the timing of signals coming from themultiple WTRUs is within a tolerance range of the receiver, timepre-correction may be needed to help ensure the synchronization ofsimultaneous ACKs received from multiple WTRUs.

The following example procedures may be used by an AP to achieve timesynchronization for simultaneous ACK transmissions. An AP may estimatethe over-the-air transmission duration between a WTRU and itself basedon individual transmissions between itself and the WTRU. Theseindividual transmissions may include, but are not limited to include,for example any of the following: single user data frame transmissionsand/or ACK(s) from the WTRU; and/or single user control frametransmissions and responses from the WTRU. For example, the AP may useroundtrip delay, IFS and/or any estimation method to compute theover-the-air transmission duration.

In an example, the AP may keep track of the estimated over-the-airtransmission duration(s) for each WTRU associated with the AP, and mayuse this information to group WTRUs for DL MU transmissions. The AP mayuse the estimated over-the-air transmission durations to compute timingadvances and/or delays to synchronize timing for transmissions from eachWTRU. For example, the AP may signal the timing advances and/or delaysto each WTRU during a DL MU transmission(s), using a modified SIG-Bfield (i.e. the SIG field that is different for each WTRU that is arecipient of the downlink transmission). The timing advances and/ordelays (also referred to as timing pre-correction) may be quantized. TheDL MU transmission may use, but is not limited to use, any of thefollowing transmission techniques: DL MU-MIMO sub-channelizedtransmission; coordinated orthogonal block-based resource allocation(COBRA) transmission; OFDMA transmission; and/or any simultaneous DL MUtransmission. The expected ACK for the DL MU transmission including thetiming pre-correction information may be any type of simultaneous UL MUACK and/or BA.

In an example, each WTRU may receive the DL MU transmission and decodethe timing pre-correction information by decoding SIG-B information.Each WTRU may receive and process the rest of the DL MU transmission byreceiving and processing the rest of the DL packet. After successfullyreceiving and processing the rest of the DL packet, each WTRU may adjustthe timing of the ACK transmission, which may include, but is notlimited to include, any of the following: if there is no timing advanceinformation, the ACK may be sent after a SIFS duration; if the value ofthe timing advance is a time duration τ, then the ACK may be sent aftera duration of SIFS−τ; and/or if timing advance is −τ (i.e. a timingdelay), then the ACK may be sent after a duration of SIFS+τ.

Mechanisms and procedures for frequency synchronization for simultaneousACK transmissions are described herein. Example procedures may includesynchronizing carrier frequencies of ACKs received at an AP frommultiple WTRUs. Frequency synchronization may be used to maintainorthogonality in frequency of each ACK. Once signals from multipletransmitters (e.g., multiple WTRUs) are in air and are combinedtogether, it becomes challenging to correct the carrier frequency foreach signal individually. Frequency pre-correction may be used to helpensure the frequency synchronization of simultaneous ACKs from multipletransmitters (e.g., multiple WTRUs) received at receiver (e.g., an AP)and to ensure that the carrier frequency of the simultaneous signalscontaining the ACKs are within a tolerance range of receiver.

Example procedures may be used by an AP to achieve synchronization infrequency for simultaneous ACK transmissions. For example, the AP mayestimate the frequency offset of each carrier frequency using individualtransmissions from each the WTRU, which may include, but is not limitedto include, any of the following: the estimation may include a coarsefrequency offset and/or a fine frequency offset; the individualtransmissions may include SU control and/or data transmissions in theUL; the AP may use a portion of a preamble of the individualtransmissions (e.g., L-STF, L-LTF, HT-STF, HT-LTF, VHT-STF or VHT-LTF,or corresponding fields in later generation WLAN implementations);and/or the AP may use any method to estimate carrier frequency offset.

In another example procedure used by the AP for synchronization, the APmay keep track of the estimated carrier frequency offset for each WTRUwith which it is associated, and may use this information to group WTRUsfor downlink MU transmission. In another example, the AP may calculate afrequency pre-correction for each WTRU, for example, based on theestimated carrier frequency offsets for each WTRU.

In another example, the AP may signal frequency pre-corrections to eachWTRU during a DL MU transmission using, for example, a modified SIG-Bfield (i.e. the SIG field that is different for each WTRU which wererecipients of the downlink transmission). The frequency pre-correctionsmay be quantized. The DL MU transmission may be, but is not limited to,any of the following transmission techniques: a DL MU-MIMOsub-channelized transmission; COBRA transmission; OFDMA transmission;and/or any other simultaneous DL MU transmission. The expected ACK mayof any type of simultaneous MU UL ACK.

In another example, Each WTRU may receive the MU downlink transmissionand decode the frequency pre-correction information, for example, bydecoding the SIG-B information. In another example, after successfullyreceiving and processing the rest of the packet, each WTRU maypre-correct the carrier frequency. As an example of pre-correction bythe WTRU, if the frequency pre-correction received at the WTRU from APis δ (e.g., δ may be any positive or negative value or 0), then the WTRUmay transmit an ACK back to the AP (e.g., using techniques describedherein) using carrier frequency f−δ, where f is the original carrierfrequency for the transmission.

As another example of UL AC aggregation in the code domain, UL ACKaggregation in the code domain may be combined with UL MU transmissions.With the use of UL OFDMA and/or UL-MIMO (e.g., in IEEE 802.11ax), UL ACKaggregation, in response to DL MU transmission, may be performed in thecode domain and may be combined with UL MU transmissions.

Example mechanisms and methods for UL ACK aggregation in the spatialdomain are described herein. Example approaches to UL ACK aggregation inthe spatial domain may include, but are not limited to include, any ofthe following: spatial-orthogonal transmission using beamforming; and/ormulti-user spatial nulling. These approaches are described in detailbelow.

According to an example approach, spatial orthogonal transmission for ULACK aggregation may use beamforming. The simultaneous transmission of ULACKs may use spatial domain techniques. In an example, a precoding maybe applied at each WTRU to create orthogonal spatial directions suchthat UL ACKs may be aggregated and transmitted simultaneously.

FIG. 12 shows a signaling diagram of a simultaneous UL ACK transmissionprocedure 1200 using spatial orthogonal transmission. FIG. 12 includesan AP 1205 in communication with WTRUs 1201, 1202 and 1203 overrespective channels with channel matrices H₁, H₂, and H₃. In the exampleof FIG. 12, the AP 1205 may have estimated the channel state information(CSI) of each channel with channel matrix H₁, where i=1−n, in a previousuplink communication with each corresponding WTRU 1201, 1202 and 1203.The AP 1205 may assign each WTRU 1201, 1202, and 1203 to the same groupfor simultaneous UL ACK transmissions. The AP may 1205 may designate abeamforming vector design order and/or spatial constraints for each WTRU1201, 1202, and 1203. The beamforming vector design order may beconsequential, as beamforming for the first WTRU 1201 may be based on asingular value decomposition (SVD) and may not have any spatialconstraints. Beamforming for a second WTRU 1202 may steer itstransmission direction such that it is orthogonal to the beamformingvector of the first WTRU 1201. Beamforming for a third WTRU 1204 maymake its beamforming vectors orthogonal to the previously designed twobeamforming vectors, and so forth.

In the example shown in FIG. 12, each WTRU 1201, 1202, and 1203 mayperform channel estimation of its corresponding channel with channelmatrix H_(i) (i=1, 2, 3) for the DL transmission. Each WTRU 1201, 1202,and 1203 may calculate its corresponding beamforming vector v_(i) (i=1,2, 3) based on its DL channel estimate and/or its order. After the DLtransmission is complete, the WTRUs 1201, 1202, and 1203 maysimultaneously transmit their ACKs 1208 ₁, 1208 ₂ and 1208 ₃,respectively, using the calculated beamforming vectors v_(i) (i=1, 2,3), which may occur after deferring by a SIFS (or other interframespacing) duration. The ACKs 1208 ₁, 1208 ₂ and 1208 ₃ are received as amixed UL ACK signal 1208 ₁, 1208 ₂ and 1208 ₃ at the AP.

On receiving the mixed UL ACK signal 1208 ₁, 1208 ₂ and 1208 ₃, the AP1205 may make i copies (e.g., 3 copies in FIG. 12) of the received mixedUL ACK signal 1208 ₁, 1208 ₂ and 1208 ₃ and may apply combining vectorsmatched to H_(i)v_(i) (e.g., H₁v₁, H₂v₂ and H₃v₃ in the example of FIG.12) to extract an individual ACK from each copy of the received signal1208 ₁, 1208 ₂ and 1208 ₃, respectively.

In FIG. 12, all three WTRUs 1201, 1202, and 1203 may have N antennas(e.g., N≥1) and the AP may have M≥N antennas. The channel matrices H_(i)(i=1, 2, 3) may be N×N channel matrices between WTRU 120 i and the AP1205. The symbols of the ACK frames 1208 ₁, 1208 ₂ and 1208 ₃ at eachWTRU 1201, 1202, 1203 may be carried by the N×1 beamforming vector v_(i)(i=1, 2, 3), respectively. The beamforming vectors v₁, v₂, and v₃ may bedetermined or generated such that the effective channel vectors H₁v₁,H₂v₂ and H₃v₃ are orthogonal to each other (an example orthogonality ofchannel vectors H₁v₁, H₂v₂ and H₃v₃ is shown in FIG. 12).

The beamforming vectors v₁, v₂, and v₃ may be calculated one by one, forexample by each WTRU 1201, 1202, and 1203. For the first vector v₁, nospatial restrictions may be imposed. The SVD decomposition of channelmatrix H₁ may be given by the following:H ₁ =U ₁Σ₁ W ₁ ^(H)  Equation 1where U₁ and W₁ may unitary matrices and Σ₁ may include the singularvalues on the diagonal in decreasing order. Denoting the first column ofW₁ as W₁(1), it may be that v₁=W₁(1), which corresponds to the largestsingular value of H₁.

Vector v₂ may be calculated (e.g., by WTRU 1202) to adjust the effectivechannel H₂v₂ in a direction that is orthogonal to H₁v₁. With a unitpower constraint on v₂, the design equations of v₂ may be given by:H ₁ v ₁ ⊥H ₂ v ₂,∥v ₂∥₂=1,  Equation 2where ⊥ indicates that the two vectors are perpendicular (and henceorthogonal) to each other.

The beamforming vector v₃ may similarly be calculated (e.g., by WTRU1203) such that the effective channel H₃v₃ is orthogonal to both H₁v₁and H₂v₂. Accordingly, the design equations of v₃ may be expressed asfollows:H ₂ v ₂ ⊥H ₃ v ₃,H ₁ v ₁ ⊥H ₃ v ₃,∥v ₃∥₂=1.  Equation 3

Thus two equations may be solved in order to calculate beamformingvector v₂. Similarly, three equations may be solved in order tocalculate the beamforming vector v₃. The beamforming vectors v₁, v₂, andv₃ may be N dimensional, where N may be refer to the number of antennasat a corresponding WTRU (e.g. WTRU 1201, 1202, and/or 1203). At WTRU1203, there may be N elements of v₃ to be determined and threeequations. As long as N≥3, at least one solution may be found. Likewise,to find a solution of the two equations at WTRU 1202, at least 2antennas may be needed. As a result, N≥3 antennas at each WTRU may beused.

More generally, if it is desired for K>3 WTRUs to simultaneouslytransmit ACKs to the AP using a spatial orthogonal method, thebeamforming vector may need to be calculated for the k-th WTRU under kconstraining equations, which may be expressed by the following:H ₁ v ₁ ⊥H _(k) v _(k),H ₂ v ₂ ⊥H _(k) v _(k),. . . .H _(k-1) v _(k-1) ⊥H _(k) v _(k),∥v _(k)∥₂=1.  Equation 4In this case, K antennas may be used at each WTRU in order to guaranteethat it possible to solve for the expected beamforming vector for eachWTRU.

Other approaches for aggregating a UL ACK such that multiple WTRUs maysimultaneously send their ACKs may include implementing a set ofreceiver filters to de-multiplex each WTRU's ACK from the receivedsignal.

Another example approach to UL ACK aggregation in the spatial domain mayinclude a MU spatial nulling receiver that may de-multiplex each WTRU'sACK from the received signal. FIG. 13 shows a block diagram of anexample receiver structure 1300 at an AP using a spatial nulling schemefor UL ACK aggregation.

In the example scenario of FIG. 13, L WTRUs may transmit L ACKsconcurrently to the associated AP, denoted by v_(l)s_(l) for l=1 . . .L. Each WTRU may include M antennas, and the AP may include N antennas.A channel between the l-th WTRU and the AP may be denoted bycorresponding channel matrix H_(l)∈

^(N×M), (l=1 . . . L).

In an example, a block diagonalization technique may be employed toseparate the concurrent ACKs. For example, H _(l) may be used to denotea composite channel matrix consisting of all the UL MIMO channels exceptH_(l), which may be denoted as follows:H _(l)=[H ₁ ,H ₂ , . . . ,H _(l−1) ,H _(l+1) , . . . ,H _(L)].  Equation5

The spatial nulling scheme 1300 may employ L filters 1304 _(l) . . .1304 _(L) for the L WTRUs. The l-th receiver filter with associatedmatrix G_(l)∈

^(N×N) may be designed in the null space of H _(l). The filtering byreceiver filters 1304 _(l) . . . 1304 _(L) may remove or eliminate theinterference from other WTRUs. This spatial constraint may use a numberof antennas at the AP of N>(L−1)M.

The SVD of the composite channel matrix H _(l) may be denoted asfollows:H _(l)=[U _(s,l) U _(n,l)]Σ_(l) W _(l) ^(H)  Equation 6where U_(n,l)∈

^(N×[N−(L−1)M]) may include the last N−(L−1)M left eigenvectors of H_(l), which may mean that the column vectors of U_(n,l) are anorthogonal basis of the null space of H _(l). Thus, U_(n,l) ^(H) H_(l)=0. It may be that the AP has CSI of all UL MIMO channel matrices,H₁, H₂, . . . , H_(l). Thus, the receiver filter matrix G_(l) of WTRU l,for l=1 . . . L, may be chosen as G_(l)=U_(n,l)U_(n,l) ^(H).

At the transmitter of each WTRU l for l=1 . . . L, CSI may not beneeded. Only one spatial stream may be used to transmit the ACK fromeach WTRU. As a result, the information symbol s_(l) at WTRU l (l=1 . .. L) may be transmitted with equal weight at each of the M antennas;that is, using the same beamforming vector v_(l)=1/√{square root over(M)}[1, 1, . . . , 1]^(T) at each WTRU l for l=1 . . . L.

The received signal y at the AP may be denoted as follows:y=Σ _(i=1) ^(L) H _(i) v _(i) s _(i) +n  Equation 7with n denoting an n-dimensional additive noise.

All L interference nulling matrices may be written together to form ade-multiplex matrix G=[G₁ ^(T), G₂ ^(T), . . . , G_(L) ^(T)]^(T). Thede-multiplexed receive signal z may be expressed as follows:

$\begin{matrix}\begin{matrix}{z = {{G{\sum\limits_{i = 1}^{L}{H_{i}v_{i}s_{i}}}} + n}} \\{= {\quad{{{\begin{bmatrix}G_{1} \\G_{2} \\\vdots \\G_{L}\end{bmatrix}\left\lbrack {H_{1},H_{2},\ldots\mspace{14mu},H_{L}} \right\rbrack}{{diag}\left( {v_{1},v_{2},\ldots\mspace{14mu},v_{L}} \right)}s} + {\left\lbrack \begin{matrix}G_{1} \\G_{2} \\\vdots \\G_{L}\end{matrix} \right\rbrack n}}}} \\{= {{\left\lbrack \begin{matrix}{G_{1}H_{1}v_{1}} & \; & \; & \; \\\; & {G_{2}H_{2}v_{2}} & \; & \; \\\; & \; & \ddots & \; \\\; & \; & \; & {G_{L}H_{L}v_{L}}\end{matrix} \right\rbrack\left\lbrack \begin{matrix}s_{1} \\s_{2} \\\vdots \\s_{L}\end{matrix} \right\rbrack} + {\left\lbrack \begin{matrix}G_{1} \\G_{2} \\\vdots \\G_{L}\end{matrix} \right\rbrack n}}}\end{matrix} & {{Equation}\mspace{14mu} 8}\end{matrix}$where s=[s₁, s₂, . . . , s_(L)]^(T).

The l-th received ACK signal may be separated from other ACK signalsbecause G_(l)H_(k)=0, for ∀k≠l. The l-th received ACK signal may berepresented by:

$\begin{matrix}\begin{matrix}{z_{l} = {{G_{l}H_{l}v_{l}s_{l}} + {G_{l}n}}} \\{= {{q_{l}s_{l}} + {G_{l}n}}}\end{matrix} & {{Equation}\mspace{14mu} 9}\end{matrix}$where q_(l) is the effective vector channel for s_(l).

The combining vector p_(l)=q_(l) ^(H)/∥q_(l)∥₂ ², 1306_(l), for l=1 . .. L, may be applied to signal z_(l) to obtain the symbol ŝ_(l) (l=1 . .. L), that is an estimate of the symbol transmitted by correspondingWTRU l, as follows:ŝ _(l) =s _(l)+[q _(l) ^(H) G _(l) n]/∥q _(l)∥₂ ²  Equation 10

Procedures and mechanisms may be used for UL ACK aggregation for DLOFDMA and/or MU-MIMO, as described herein. UL ACK aggregation may reducefeedback overhead for simultaneous DL transmissions, for example in DLOFDMA and/or DL MU-MIMO, which may result in throughput (TP)improvements. In an example, each WTRU may indicate its ability tosupport UL ACK aggregation to the AP, for example, by providing anindication in the capability information field in its beacon. Acapability information indication may be included in the SIG field ofthe PPDU, for example.

For example, capability information may include, but is not limited toinclude, an indication for support for any one or more of the following:an aggregated ACK; an aggregated delayed ACK; and/or an aggregated BA.An aggregated ACK capability may include the capability of an aggregatednegative ACK (NAK) in combination with, or instead of, an ACK in thesame aggregated capability field(s). A capability information elementmay also indicate support for aggregation of UL short ACKs and/or short(data or control) frames.

In an example, DL ACK aggregation may be indicated in the capabilityinformation field of the beacon from the WTRU. DL ACK aggregation maysupport the same capabilities as UL ACK aggregation. The capabilityinformation field may include a group based UL ACK capabilityindication. For example, UL ACK aggregation may be defined for, but isnot limited to, any of the following: frequency; channel; code;sequence; time unit; and/or spatial groups, as described above.

Methods and procedures for UL aggregation are described herein. In anexample, an indication or request for UL aggregation of ACK responsesmay be indicated in a MAC information element (IE), and/or within thePHY header as an indication in the SIG information field. A request forUL aggregation of ACK responses from two or more WTRUs that haveassociated on different channels may be determined by the AP byconsidering the impact on the overall delay of the aggregatedtransmissions. For example, a request may be made for an immediatenormal ACK response for one or more WTRUs, and an aggregated ACKresponse for the remaining WTRUs, for example. In another example, arequest may be made for a delayed ACK response for one or more WTRUs,and an aggregated ACK response for the remaining WTRUs.

In an example, UL ACK aggregation may be determined or requested usingan Aggregation ACK Request (AAR) control frame. FIG. 14 shows a frameformat for an example AAR control frame 1400. The AAR control frame 1400may be sent by an AP to a WTRU, for example. The AAR control frame 1400may include, but is not limited to include, any of the following: aframe control field 1404; a duration field 1406; an RA field 1408; a TAfield 1410; an AAR control field 1412; a multi-TID control field 1414(that may include repeated information for each TID, for example);starting sequence control (SSC) fields e.g., there may be two to eightSSC fields); and FCS field(s) 1416. The multi-TID control field 1414 mayindicate that the AAR control frame supports multiple aggregation ACKsessions for one or more channels.

FIG. 15 shows a frame format for an example aggregated ACK (AA) responseframe 1500. The AA response frame 1500 may be sent by a WTRU to an AP,for example. The AA response frame 1500 may include, but is not limitedto include, any of the following: a frame control field 1504; a durationfield 1506; an RA field 1508; a TA field 1510; an AA control field 1512;SSC field(s) 1514; an AA bitmap field 1515; and FCS field(s) 1516. TheAA bitmap field 1515 may indicate the receive status for up to eight MACservice data units (MSDUs) carried on up to eight channels, for example.

FIG. 16 shows a frame format for an example block ACK (BA) AA responseframe 1600. The BA AA response frame 1600 may be sent by a WTRU to anAP, for example. The BA AA frame 1600 may include, but is not limited toinclude, any of the following: a frame control field 1604; a durationfield 1606; an RA field 1608; a TA field 1610; A BA control field 1612;an AA control field 1613; SSC field(s) 1614; a BA/AA bitmap field 1615;and FCS field(s) 1516. In an example, a concatenation of BAs from up toeight aggregated channels may be included the BA AA frame 1600. In anexample, the BA AA frame 1600 may be similar to the AA frame 1500 exceptthat a BA control field 1612 and BA/AA bitmap field 1615 may be includedfor each aggregated ACK channel defined by the AA bitmap 1615.

In an example, the request or indication for UL aggregation of ACKresponses may be carried on a primary channel, and the indication forACK responses of WTRUs that have associated on the primary channeland/or secondary channels may be provided. For example, the indicationfor ACK responses from secondary channels may be provided by a bitmap(e.g., the bitmap may be four to eight bits in length and include alogical value of 1/0 in each bit location), which may provide an ACKresponse request for WTRU(s) associated on each channel. The aggregatedACK responses may be carried on one or more sub-channels within theprimary channel, and/or on one or more secondary channels.

In an example, if there is a primary channel and a secondary primarychannel, the channel for which the WTRU, or group of WTRUs, receivedtheir channel resource allocations may be reserved for aggregated ACKresponses from those WTRU(s). In another example, the preferred channelfor aggregated ACK responses for a particular group of WTRUs, orassociated Group ID, may be indicated in an information element withinthe MAC header, frame body or elsewhere (e.g. in a frame from the AP).

In an example, if one or more ACK responses indicate a negativeacknowledgment (NAK), the responses that contain a NAK may take priorityfor transmission over associated ACK responses. A lack of response for achannel or sub-channel in an aggregated ACK response may also beconsidered a NAK response. The transmitter (e.g., AP) may elect to pollWTRUs for which a response has not been received for an explicit ACK orNAK response.

FIG. 17 is a flow diagram of an example UL aggregated ACK responseprocedure 1700. At 1702, an AP may send an beacon indication or requestfor UL ACK aggregation, 1702 (FIG. 14 shows an example request frame).At 1704, the AP may receive from the WTRUs an UL aggregated ACK responseframe, or MU ACK response frame, (FIGS. 15 and 16 show example responseframes), in which UL aggregated ACK response(s) may be indicated in anAggregation ACK Request Control Frame (AARCF) bitmap. At 1706, the APdetermines if the MU ACK response frame was sent on a primary channel.

If the MU ACK response frame was sent on a primary channel, then theWTRUs for which the group ID is associated with a secondary channel mayrespond on a secondary channel, 1712. If the MU ACK response frame wasnot sent on a primary channel, then the AP may check for a beaconindication to respond from at least one WTRU on a secondary channel,1708. If a beacon indication is detected on a secondary channel, thenthe WTRUs for which the group ID is associated with a secondary channelmay respond on a secondary channel, 1712. If a beacon indication is notdetected on a secondary channel, the WTRUs for which the group ID isassociated with the primary channel may respond on the primary channel,1710.

Example mechanisms and methods for DL ACK aggregation are describedherein, and may be used for UL OFDMA and/or UL MU-MIMO. Approaches to DLACK aggregation may include, but are not limited to include, any of thefollowing: MU BA in DL; and/or reuse of any of the UL ACK aggregationtechniques discussed herein for DL ACK. MU and multi-WTRU may be usedinterchangeably herein, and multi-WTRU BA may equivalently implymulti-WTRU BA/ACK in all examples given herein. Additionally, channel,sub-channel, and/or resource unit may be used interchangeably herein.Additionally, user, WTRU, and STA and similarly multi-user (MU) andmulti-WTRU (or multi-STA), may be used interchangeably herein.

An MU (or multi-WTRU) BA may be used by the AP to acknowledge multipleWTRUs. FIG. 18 shows a signaling diagram of an example MU BA procedure1800. Although FIG. 18 (and similarly any other figure described herein)herein may show the vertical axis as frequency, any channel scheme maybe applied for transmission that may not be limited to the frequencyversus time domains. For example, channels (e.g. resource units and/orsub-channels) may be distinguished in the frequency and/or spatialdomain, using OFDMA and/or MU-MIMO, for example.

In this example, WTRUs 1801, 1802, 1803, and 1804 may simultaneouslytransmit UL respective frames (or packets) 1810 ₁ . . . 1810 ₄ to AP1805, where the UL frames 1810 ₁ . . . 1810 ₄ may be UL-MIMO or UL-OFDMAtransmissions, for example. The WTRUs 1801, 1802, 1803, and 1804 may padbits (shown with the dotted line in FIG. 18) at the end of eachrespective packet 1810 ₁ . . . 1810 ₄ in order to (approximately) alignthe packets in time. In another example, the WTRUs 1801, 1802, 1803, and1804 may not pad bits at the end of the packets 1810 ₁ . . . 1810 ₄.

In another example, the packets or frames 1810 ₁ . . . 1810 ₄transmitted by the WTRUs 1801, 1802, 1803, and 1804 may be aggregatedwith UL ACKs/BAs or delayed UL ACKs/BAs (not shown) in response to a DLMU transmission such as DL OFDMA or DL-MIMO transmission (not shown).After the termination of the UL simultaneous transmission of packets1810 ₁ . . . 1810 ₄, there may be an IFS duration such as SIFS or RIFS.The AP 1805 may send a MU BA frame 1808 to WTRUs 1801, 1802, 1803, and1804. Various example MU BA transmission methods and frame formats aredescribed herein.

Example mechanisms and procedures for MU BA include a multi-dimensional(MD) MU BA procedure. In an example, An MD MU BA frame may betransmitted over the entire available bandwidth using all availableresource units. The MD MU BA frame may be transmitted using a broadcasttransmission scheme, such as an omnidirectional transmission scheme,which may allow all users in the BSS to receive the MD MU BA frame.

In an example, the MU BA MAC frame may be multiplexed in thehigh-efficiency (HE) PPDU by DL MU-MIMO or DL OFDMA. For example, the MUBA frame may be transmitted or repeated over a WTRU-specificsub-channel, such as the sub-channel or resource units that the WTRUused for UL data transmission (e.g., to simplify the implementation atthe WTRU). In an example, the AP may prepare a MD MU BA frame in any oneor more of the following example circumstances: where the AP receives aUL MU transmission from multiple WTRUs; and/or where the AP receivestransmissions with delayed BA protocol, where the transmissions may havebeen previously received by the AP from multiple WTRUs.

FIG. 19 shows a frame format of an example MD MU BA frame 1900. The MDMU BA frame 1900 may include, but is not limited to include, any of thefollowing fields: a frame control field 1904; a duration field 1906; anRA field 1908; a TA field 1910; an MU BA control field 1912; an MU BAinformation field 1914; and/or an FCS 1916.

The MD MU BA frame 1900 may be indicated in the frame control field 1904using, for example, any one or more of the following methods: a subtypemay be defined for MD MU BA control frame (e.g., under control type(01), the subtype for MD MU BA control frame may be any of the valuesbelonging to [0000, 0011]; a type may be defined (e.g., type=11 may havecorresponding type description as MU BA); and/or reusing a BA type andsubtype, where the RA field 1908 may be revisited, as described below,after detecting that the frame 1900 is an MU (Multi-WTRU) BA frame (maybe signaled later in the frame 1900).

The RA field 1908 may include addresses of the recipient WTRUs, and mayinclude for a group address(es) that represent multiple WTRUs. The RAfield 1908 may or may not be a MAC address. The RA field 1908 mayaddress a recipient WTRU using any one or more of the following examplemethods. In an example method, the RA field 1908 may carry the group ID,which may be combined with (full or partial) AID to identify theintended recipient WTRU (receiver) of the BA information field 1914 (thepartial AID may be present the corresponding WTRU subfield 1926 _(i) ofthe MU BA info field 1914). In another example method, the RA field 1908may carry the group ID, which may be combined with (partial) AID toidentify the intended receiver of the MU BA information field 1914 (thepartial AID may present in the MU BA control field 1912 such as in theMU bitmap subfield 1922 and/or the reserved subfield 1924).

In another example method, the RA field 1908 may be the MAC address orAID of the first (WTRU 1) or last (WTRU k) WTRU of the MU BA informationfield 1914. The RA field 1908 may be used to derive the address or AIDof each WTRU carried in MU BA info field 1914 by a pre-defined rule. Inanother example method, the RA field 1908 may be re-interpreted asmultiple WTRUs' AID. For example, a 48 bit RA may support three WTRUswith 16 bit AID each. In another example, a 48 bit RA may support fourWTRUs with a 12 bit AID each. In another example, a 48 bit RA may usethe first M bits to indicate the group ID, and 48-M bits to indicate(partial) AID for multiple WTRUs.

In another example method, the RA field 1908 may present nothing, and/ormay fill a pre-defined sequence. The AID present for each WTRU may bepresent in each WTRU subfield 1926 l . . . 1926 k to be uniquelyaddressed. In another example method, the MD MU BA frame 1900 maycontain only one BA info field 1914, and the RA field 1908 may includethe address of the WTRU. In another example method, if the MD MU BAframe may contain more than one BA info field 1914 (or an MU BA infofield 1914), and the RA field 1908 may include a group address for agroup of multiple WTRUs. The group address may be, for example, a MACaddress that has the group bit equal to 1. The group address may bereserved by the BSS and assigned to certain WTRUs by the BSS.

The TA field 1910 may include an address of the transmitter (e.g., theAP), which may be, for example, the BSSID of the transmitter.

The MU BA control field 1912 may include, but is not limited to include,any one or more of the following subfields: BA ACK policy field 1918;multi-TID field 1920; compressed bitmap field (not shown); MU bitmapfield 1922; and/or reserved subfield(s) 1924. The BA ACK policy subfield1918 may indicate a normal ACK or delayed ACK. The multi-TID subfield1920 may indicate multiple TIDs or the same (a common) TID. The TIDcompressed bitmap field (not shown) may indicate that the MU BA frame1900 contains the compressed bitmap (i.e., 8 octet block ACK bitmap) orthe uncompressed bitmap (i.e., 128 octet block ACK bitmap). In anexample, the MU bitmap subfield 1922 may be used to indicate a multi-STABlock ACK that may not be sent under Delayed and/or HT-delayedagreements. The MU bitmap subfield 1922 may be used to indicate theacknowledgement for each user (e.g., WTRU) identified in the RA field1908. In an example, it may be possible to acknowledge a subset of WTRUsin a group of WTRUs. The MU bitmap subfield 1922 may contain N bits,where N is the number of WTRUs signaled in the RA field 1908. Each bitmay be used to indicate whether the BA information (e.g., 1926 i) ofthat user/WTRU (e.g. WTRU i) is included in the MD MU BA control frame1900. The reserved field 1924 may include the number of WTRUs in MU BAinformation field 1914.

The MU BA information field 1914 may include subfields for WTRUs l . . .k. The total number of WTRUs k included in the MU BA Information field1914 may depend on the MU bitmap field 1922 defined in the MU BA controlfield 1912. Each WTRU subfield 1926 l . . . 1926 k may include astarting sequence subfield 1928 i and/or a BA bitmap subfield 1930 i(for i=1 . . . k).

The MU BA information field 1914 may be formed using any one or more ofthe following techniques. In an example, a fixed length may be used foreach WTRU subfield 1926 _(l) . . . 1926 _(k). In an example, per-WTRUinformation may be inserted before the starting sequence control field1928 _(l) . . . 1928 _(k) for each WTRU subfield 1926 _(l) . . . 1926_(k). The per-WTRU information may include, but is not limited toinclude, any of the following: AID or (partial) AID; BA/ACK indication;and/or TID value.

In another example, variable lengths may be used for different WTRUsubfields 1926 ₁ . . . 1926 _(k), which may be prepended by apre-defined sequence or delimiter used to define the WTRU subfield'sposition and length inside the aggregated MU BA Information field 1914.In an example, padding may be used after each WTRU's BA bitmap 1930 ₁ .. . 1930 _(k). The pre-defined sequence may be indicated in the MACheader or implicitly determined, for example. In an example, differentWTRU subfields 1926 ₁ . . . 1926 _(k) may be prepended by a per-WTRUinformation that may determine the length of each WTRU subfield. Forexample, if an ACK indication is present in a per-WTRU info field 1926_(i), then the starting sequence control 1928 _(i) and/or BA bitmap 1930i may not be present. In another example, if a BA indication is presentin the per-WTRU info field 1926 _(i), then the starting sequence control1928 _(i) and the BA bitmap 1930 _(i) may be present.

Example AP procedures for MD MU BA are described herein. In an example,the AP may receive an UL MU transmission that may contain multiple(data) packets from one or more WTRUs. The AP may detect thetransmitters (e.g., WTRUs) of the detected packets and may and prepare afirst dimension bitmap (e.g. MU bitmap 1922 in FIG. 19) using any one ormore of the following example procedures. The AP may check the groupaddress (for example group ID), that may be carried in the UL MU PLCPheader, noting potential transmitters. The group ID may indicate Mpotential transmitters. The AP may receive multiple packets, and eachpacket may be in the AMPDU format. The AP may obtain the MAC addressfrom each packet. The total number of transmitters may be denoted by k,where k≤M. The AP may prepare a first dimensional bitmap (i.e. MUbitmap), according to the above information. The MU bitmap may contain Mbits, where each bit may represent whether the corresponding WTRU in thegroup has a BA in the second dimension (e.g., “1” to indicate a BA inthe second dimension, and “0” to indicate absence of BA in the seconddimension). In the example shown in FIG. 19, the MU bitmap 1922 maycontain k “1” s.

In an example, the AP may generate a second dimension bitmap, which maybe denoted as BA bitmap, by checking received packet(s) from each WTRU.The received packet(s) may be in AMPDU format (i.e. an aggregation ofmultiple MPDUs) or MPDU format (non-aggregate MPDUs). In the examplecase that A-MPDU format is used, the received packet (AMPDU) may be fromone WTRU. It may be possible that a particular WTRU has two or morepackets (A-MPDUs). The AP may prepare the second dimension bitmap usingany one or more of the following procedures: the AP may collect all thepackets from the particular WTRU; The AP may check the FCS of each MPDU;and/or The AP may prepare a second-dimension BA bitmap for theparticular WTRU. In the example case that MPDU format is used, the APmay prepare the second dimension bitmap by generating a normal ACK thatmay be indicated by pre-defined bitmap or dummy bitmap. For example, apre-defined 2-bit bitmap may be used to support up to 4 ACKacknowledgement states (e.g., ACK, NACK, DTX and reserved.)

In an example, the AP may prepare a MU BA info field and may form an MDMU BA frame, such as the MD MU BA frame 1900 shown in FIG. 19. In anexample, if a WTRU subfield with a fixed length is in MU BA info field,the AP may insert k WTRU subfields into the MU BA info field in apre-defined order, for example from WTRU 1 to WTRU k. In an example, ifa WTRU subfield with a variable length is in MU BA info field, the APmay insert k WTRU subfield(s) with pre-defined sequences or delimitersand/or padding into the MU BA info field.

Example WTRU (STA) procedures for MD MU BA are described herein. A WTRUaddressed by the AP may use the pre-defined bitmap, as discussed above,to allocate its ACK/BA response in the ACK/BA frame. The WTRU mayreceive a DL MD MU BA frame, which may or may not be a response to theWTRU. The WTRU may check the frame control field, and recognize theframe as an MD MU BA frame. The WTRU may check the second address field(or the first address field), which may contain a BSSID. If the WTRU isnot associated with the BSSID, the WTRU may not be a potential receiverof the MD MU BA frame. The WTRU may check the first address field (orthe second address field), which may be re-interpreted as a groupaddress (for a group of WTRUs) in the MD MU BA frame.

In further examples, the WTRU may check the group address. If the WTRUis the (or one of) addressed WTRU(s), then the WTRU may decode thereceived MD MU BA frame; otherwise, the WTRU may discard the MD MU BAframe. The WTRU may check the first dimension bitmap (i.e. MU bitmap1922 in FIG. 19) and pay perform any of the following: if the bitcorresponding to the WTRU in MU bitmap is equal to “1”, it may indicatethe WTRU in the MU group may receive an ACK/BA in the second-dimensionbitmap, in which case the WTRU may check the 2^(nd) dimension bitmap(i.e. BA bitmap); and/or if the bit corresponding to the WTRU in MUbitmap is equal to “0”, it may indicate that the packet from the WTRUwas not successfully decoded, and thus there is no need for the WTRU tocheck its ACK/BA in the second dimension bitmap.

In further examples, the WTRU may check the second dimension bitmap(i.e. BA bitmap 1930 _(i) in FIG. 19) to obtain its BA using any one ormore of the following methods: in a case where the WTRU subfield has afixed length MU BA info field, the WTRU may read its second-dimension BAbitmap based on the bit location in the MU Bitmap or pre-defined order;and/or in a case where the WTRU subfield has a variable length MU bitinfo field, the WTRU may perform a correlation with the pre-definedsequence or delimiter to determine the location and length of thesecond-dimension BA bitmap for this WTRU and then may read the bitmap.

Example MU BA methods may include broadcast MU BA procedures. In anexample, a 64×16 bit uncompressed BA bitmap may be reusing the 16 bitsthat may be used for a MSDU fragment and using them for an indication ofthe WTRU identity for MU ACK aggregation. This method may support up to64 MPDUs for each WTRU, and up to 16 WTRUs. The 16 bits in the BA bitmapmay include, but is not limited to include, any of the following exampleelements: the MAC address of each WTRU for MU BA aggregation; and/or theCDMA code index or sequence applied to each WTRU's BA to support MU ACKaggregation.

In an example, an indication that a BA is an MU version BA may beindicated to MU WTRUs to distinguish from, for example, an uncompressedBA for a SU. This indication may be made in the frame control fieldusing any one or more of the following techniques: a type may bedefined, for example type=11, and the corresponding type description maybe MU BA; and/or a subtype may be defined, for example under the controltype (01), where the subtype may equal any value belonging to [0000,0011].

Example MU BA methods may include broadcasted null data packet (NDP) MUBA procedures. According to an example, an NDP frame(s) may be used toacknowledge multiple users simultaneously. An NDP frame may contain aPLCP header only, and may not have a MAC body included. An NDP MU ACKframe may be broadcast to all users. The NDP MU ACK frame may carryinformation by rewriting the SIG field in the PLCP header. In anexample, the SIG field may be transmitted over a basic sub-channel unit,and/or repeated on the rest of the sub-channels. In an example, the SIGfield may be transmitted over the entire bandwidth. The SIG field mayinclude, but is not limited to include, any of the following fields: anNDP MU ACK body field; an NDP MAC frame indication field; a CRC field;and/or a tail field for a convolutional code.

FIG. 20 shows a frame format for an example NDP MU ACK body field 2000.The NDP MU ACK body field 2000 may include, but is not limited toinclude, any of the following fields (subfields): an NDP MAC frame typefield 2002; an MU mode field 2004; a color/AP address field 2006; agroup ID field 2008; an MU ACK Bitmap field 2010; a more data field2012; and/or reserved subfield(s) 2014.

The NDP MAC frame type subfield 2002 may indicate that the NDP MAC frame(i.e. full frame for the NDP MU ACK body field 2000) is an NDP MU ACKframe. The MU mode subfield 2004 may be used to indicate whether thetransmission is for OFDMA, MU-MIMO and/or single user, for example. Thecolor/AP address subfield 2006 may contain the identity of the AP. Forexample, color bits and/or the AP address may be used, where the APaddress may be a (partial) BSSID of the AP. The group ID subfield 2008may be used to signal the group ID. The MU ACK bitmap subfield 2010 maybe used to carry the ACK information for each user (WTRU) or resourceblock. If the AP successfully decodes the packet in the NDP MAC framefor a certain WTRU or on a certain resource block, the AP may set a bitto “1” in the MU ACK bitmap 2010 for the corresponding WTRU (user) orresource block. Otherwise, the AP may set the bit to “0” in the MU ACKbitmap 2010 for the corresponding WTRU (user) or resource block.

In an example, the more data subfield 2012 may include a bitmap and eachbit of the bitmap may correspond to a particular WTRU (user) or resourceblock. A bit in the bitmap may be set to “1” to indicate that the AP hasmore buffered data for the associated WTRU (user) or for a user on theassociated resource block. In another example, the MU ACK bitmap 2010may be used to indicate that the transmission opportunity (TXOP) may beextended and a DL transmission may follow the NDP MU ACK frame. Inanother example, the more data subfield 2012 may be a bit, which may beused to indicate that a DL transmission to the same group of WTRUs mayfollow.

Example MU BA methods may include broadcasted and/or dedicated NDP MU BAprocedures. In an example method, an NDP frame may be used toacknowledge multiple users simultaneously. An NDP frame may have a PLCPheader only and no MAC body included. For example, the MAC informationmay be carried in a PLCP header in a SIG-A and/or SIG-B field. In anexample, an NDP MAC frame indication may be included in a SIG field, andthe SIG field(s) may be overwritten to carry the NDP MAC frameindication.

FIG. 21 shows a frame format for an example NDP MU BA header 2100. Theexample of FIG. 21 may use four channels or sub-channels 2102 ₁ . . .2102 ₄. Any or all of the fields shown in FIG. 21 may be part of a PLCPheader, for example. In the NDP MU BA header 2100, the SIG fields may bedivided into a common part (e.g. broadcast part) and a user-specificpart (e.g. a dedicated part). In the example shown in FIG. 21, HE-SIG-Afield(s) 2106 ₁ . . . 2106 ₄ may be the common part and HE-SIG-Bfield(s) 2110 ₁ . . . 2110 ₄ may be the user-specific part.

L-STF, L-LTF and L-SIG fields 2104 ₁ . . . 2104 ₄ may be backwardcompatible. HE-SIG-A fields 2106 ₁ . . . 2106 ₄ and HE-SIG-B fields 2110₁ . . . 2110 ₄ may be PHY header(s), and may carry PHY layer relatedsignaling information, and/or may be (partially) overwritten by MU BAinformation when used in an NDP MU frame. HE-SIG-A field(s) 2106 ₁ . . .2106 ₄ may be transmitted over basic sub-channel(s) 2102 ₁ (e.g. 20 MHzif the entire channel bandwidth is 80 MHz), and repeated on the rest ofsub-channels 2102 ₂ . . . 2102 ₄. HE-SIG-A field(s) 2106 ₁ . . . 2106 ₄may include NDP MU ACK indication(s). HE-STF, HE-LTF fields 2108 ₁ . . .2108 ₄ may be training fields for HE packet(s). HE-SIG-B fields 2110 ₁ .. . 2110 ₄ may include, but are not limited to include, any of thefollowing information: BA bitmaps; and/or partial AID(s) (PAID(s)),where an AID may be an association ID assigned by the AP when a WTRUperforms association with the AP, and a PAID may be a compressed AID.

FIG. 22 shows a frame format for an example HE-SIG-A field 2200 (e.g.,the HE-SIG-A field(s) 2106 ₁ . . . 2106 ₄ shown in FIG. 21). TheHE-SIG-A field 2200 may include, but is not limited to include, any ofthe following: an NDP indicator field 2202; an NDP MAC frame type field2204; an MU mode field 2206; an AP address field 2208; a duration field2210; a bandwidth (BW) field 2212; a more data field 2214; an NDP SIG-Bpresent field 2216; and/or reserved field(s) 2218.

The NDP indicator field 2202 (e.g. an NDP MU ACK indication) mayindicate a NDP control MAC frame. With this indication, the HE-SIG-Afield may be overwritten. The NDP MAC frame type field 2204 may be usedto indicate the NDP MU BA frame. The MU mode field 2206 may be used toindicate the MU transmission mode, which may be SU, MU-MIMO and/orOFDMA, for example. The AP address field 2208 may be a (partial) BSSIDof the transmitting AP, or another type of AP address. The durationfield 2210 may be used to indicate the duration of the transmissions.The BW field 2212 may be used to indicate the bandwidth of the NDP MU BAframe. The more data field 2214 may be used to signal whether the AP hasmore data for the group of WTRUs. The NDP SIG-B present field 2216 maybe used to indicate that an NDP-SIG-B field may follow (e.g. 1 bit).Other fields, such as a tail or CRC may be presented, although notshown.

FIG. 23 shows a frame format for an example HE-SIG-B field 2300 (e.g.,the HE-SIG-B field(s) 2110 ₁ . . . 2110 ₄ shown in FIG. 21). An HE-SIG-Bfield 2300 may be presented when the NDP SIG-B present field in HE-SIG-Ais set to 1, for example (as described in FIG. 22). HE-SIG-B field 2300may be sub-channel dedicated or user dedicated. For example, with OFDMA,each sub-channel may carry its own HE-SIG-B field (e.g., the HE-SIG-Bfield(s) 2110 ₁ . . . 2110 ₄ on sub-channels 2102 ₁ . . . 2102 ₄ shownin FIG. 21).

Each HE-SIG-B field 2300 may include, but is not limited to include, anyof the following information: PAID field 2302 may be a partialassociation identity (AID) of a receiving WTRU, and be another type ofaddress such as compressed address and/or full address; ACK field 2304may be used to carry acknowledgement (e.g., in the case of BA, it may bea bitmap; and/or reserved field(s) 2306.

In an example, the HE-SIG-A field(s) and HE-SIG-B field(s) may usedifferent modulation schemes with different FFT sizes. In anotherexample, some fields defined in the HE-SIG-A field, as described above,may be carried in the HE-SIG-B field, and vice versa.

In an example, any of the techniques for UL ACK aggregation describedabove may be used for DL ACK aggregation and/or UL MU transmission. Inanother example, UL ACK aggregation described herein may be used for DLACK aggregation in combination with a header designed for DL ACK MUaggregation for UL MU transmission. FIG. 24 shows a frame format for anexample DL ACK MU aggregation header 2400. The DL ACK MU aggregationheader 2400 may include, but is not limited to include, any of thefollowing fields: STF field 2402; LTF fields 2404 _(l) . . . 2404 _(n);SIG fields 2406 _(l) . . . 2406 _(n); and ACK fields 2408 _(l) . . .2408 _(n), where the ACK fields 2408 _(l) . . . 2408 _(n) may beaggregated using any of the techniques for UL aggregation describedherein. The use of the DL ACK MU aggregation header 2400 may reduce thecommon signaling overhead while enabling the aggregation ofWTRU-specific headers and ACKs in a DL ACK MU frame, for example.

Example techniques may be used for reusing a Multi-TID BA for MU BA. Themulti-TID BA frame format may be used for multi-WTRU BA/ACKtransmission, for example in IEEE 802.11ax. Techniques are describedherein for reusing the multi-TID BA frame format for MU (multi-WTRU)BA/ACK transmission.

In an example, the RA field may contain a receiver MAC address. With MUBA, the RA field may be redefined or reinterpreted because multiplereceivers may be involved. The RA field may be designed using, but notlimited to, any one or more of the following methods. In an example, theRA field may carry the group ID, which may be combined with (partial)AID to identify the intended receiver of the BA information field ofmulti-WTRUs. The (partial) AID may be present in a WTRU subfield of anMU BA info field, for example. In another example, the (partial) AID maybe present in an MU BA control field such as an MU bitmap field and/or areserved subfield.

In another example, the RA may be the MAC address or AID of the first(or the last) WTRU of the MU BA information field. It may be used toderive the address or AID of each WTRU carried in MU BA info field by apre-defined rule. In another example, the RA may be re-interpreted as anAID for multiple WTRUs. For example, a 48-bit RA may support three WTRUswith 16-bit AID each. In another example, a 48-bit RA may support fourWTRUs with 12-bit AID each. In another example, a 48-bit RA may use thefirst M bits to indicate the group ID, and the next 48-M bits toindicate a (partial) AID for multiple WTRUs. In another example, the RAmay present nothing, and/or may be filled with a pre-defined sequence.The new AID present for each WTRU may be present in each WTRU subfieldto be uniquely addressed.

In another example, the MD MU BA frame may contain only one BA infofield, and the RA field value may be the address of the WTRU. In anotherexample, if the MD MU BA frame contains more than one BA info field, theRA field value may be a group address. The group address may be a MACaddress that has the group bit equal to 1. The group address may bereserved by the BSS and assigned to certain WTRUs by the BSS, forexample.

Examples mechanisms and methods for MU BA signaling are describedfurther herein. In an example, the MU BA frame may be signaled in theframe to identify it as an MU BA frame, using, but not limited to, anyone or more of the following techniques. In an example, MU BA may besignaled using type, and/or subtype in the frame control field. Inanother example, MU BA may be signaled using the combination of theMulti-TID field, the compressed bitmap field and/or the GCR subfields inthe BAR control field. For example, [Multi-TID, Compressed Bitmap,GCR]=[1,1,1] may be used to indicate an MU BA frame.

In an example, the BA information field may be repeated for each user(WTRU). The number of BA information fields (or the number of intendedreceivers/WTRUs of the MU BA frame) included in the MU BA frame may besignaled, for example using, but not limited to, any one or more of thefollowing approaches: using TID_Info subfield in BA control field, whereTID_Info subfield may be reinterpreted as the number of BA informationfields; and/or using reserved bits in BA control field to signal thenumber of BA information fields.

Example mechanisms include suing partial AID in a BA information field.In an example, 11 bits in a per-TID info subfield of the BA informationfield may be used to carry an MU BA partial AID of the receiver (e.g.WTRU). The MU BA partial AID may be defined using, for example, thefollowing definitions:(dec(AID[0:10])+dec(BSSID[44:47]⊕BSSID[40:43])*2⁵)mod 2⁹; and/orAID[0:10].

A variable length BA information field may be designed using any of thefollowing example techniques. The length of the BA information field maybe variable because ACK and BA may be supported. The proceduresdescribed herein may be used by the receiver (e.g. WTRU) to identify theBA information.

FIG. 25 shows a frame format for an example MU BA control frame 2500. MUBA control frame 2500 may include, but is not limited to include, any ofthe following: a frame control field 2504; a duration and/or ID field2506; an RA field 2508; a TA field 2510; a BA control field 2512; avariable length BA information field 2514; and/or an FCS 2516. The BAcontrol field 2512 may include, but is not limited to include, any ofthe following subfields: a BAR ACK policy field 2518; a multi-TID field2520; a compressed bitmap field 2522; a GCR field 2524; a reservedfield(s) 2526 (e.g., bits B4 to B11); and/or a TID_INFO field 2528.

The variable length BA information field 2514 may include informationthat is repeated for each TID. The repeated information in the BAinformation field 2514 may include, but is not limited to include, anyof the following: an MU BA delimiter field 2530; a per-TID informationfield 2532; a BA SSC field 2534; and/or a BA bitmap field 2536.

As shown in FIG. 25, a MU BA delimiter subfield 2530 may be prepended toeach BA information field 2514 (and repeated for each TID). The MU BAdelimiter field 2530 may contain a sequence that may specify theboundary between BA information. The detailed MU BA delimiter 2530design may use, but is not limited to, any one or more of the followingexample methods. In an example method, a universal sequence or signaturemay be specified or predetermined and may be used to detect the boundaryof a BA info field by the receivers. The MU BA Delimiter subfield mayinclude, but is not limited to, any of the following: the BA/ACK length(or BA info length) for the receiver (WTRU); and/or a CRC. In anotherexample method, a WTRU (user) specified sequence or signature may beused. Each receiver may scan its own sequence or signature to obtain itsBA information. The MU BA Delimiter subfield may include, but is notlimited to, any of the following: the BA/ACK length (or BA info length)for the receiver (WTRU); and/or a CRC.

Referring back to the example in FIG. 25, the MU BA delimiter subfield2530 is shown to be followed by a per-TID info subfield 2532. In anexample, the MU BA delimiter subfield 2530 and the per-TID info subfield2532 may be combined, and the combined subfield may include, but is notlimited to include, any of the following information: asequence/signature that may defining the boundary of MU BA informationfield; a BA/ACK indication that may indicate a BA or a normal ACK in theBA information field; a receiver ID (e.g. partial AID and/or AID); aBA/ACK length that may indicate the length of the BA information for theWTRU (user); and/or a CRC field.

Example mechanisms and methods may be used to indicate a multi-WTRU (MU)BA frame. For example, in order to differentiate between a Multi-WTRU BAframe and Multi-TID BA frame, an indication may be added to the frame toindicate that it is a multi-WTRU BA. Example indication techniques mayinclude, but are not limited to include, any of the followingapproaches: an indication may be included in a frame control field, forexample, by defining a type and/or subtype; a BA type or subtype may beused for indication, where the RA field may be revisited after detectingthe frame is a Multi-WTRU BA frame (may be signaled later in the frame);and/or a GCR field may be used to signal the multi-WTRU BA.

In an example, a BAR/BA protocol may be used for a multi-WTRU BA frameand may be used with any of the MA BA mechanisms and proceduresdescribed herein. Reusing multi-TID BA for Multi-WTRU BA/ACK may includeredefining the BAR/BA protocol. An ACK policy may be used formulti-WTRUs within this multi-WTRU BA frame. For example, some users(WTRUs) may need immediate BA, and some users may permit delayed BA. Inanother example, all WTRUs within a multi-WTRU BA frame may needimmediate and/or delay BA.

Mechanisms and procedures may be used for short packet MU aggregation inthe DL, UL, and/or peer-to-peer transmissions. Short packet MUaggregation may include, but is not limited to include, any of thefollowing: short data packet MU aggregation; and/or MU aggregation forshort data packet and control frames such as ACK or short ACK.

The IEEE 802.11n and 802.11ac specifications may include aggregatedMPDUs for SU aggregation within the same burst. In MU scenarios, whereall the users (WTRUs) have small packets, the packet data units that maybe aggregated into short bursts from multiple WTRUs may be aggregated inone PPDU. This approach may be especially useful as a MAC level changefor MU aggregation of IEEE 802.11ax transmissions in high-densityenvironments. Moreover, any of the techniques for MU ACK aggregation, asdescribed herein, may be applicable to short data packet MU aggregation.

In an example, short packets of different types addressed to multipleusers may be aggregated. Short packet MU aggregation for DL, UL or P2Ptransmissions may include, but is not limited to include, any of thefollowing information: a packet header that may indicate that the dataframe is a MU aggregated data frame, as indicated for example in the PHYheader and/or MAC header; and/or a packet header may indicate a numberof users to whom the frame is addressed. The packet header may bestructured using any of the following example approaches, which may becombined in one transmission or in separate transmissions: in an examplecase where the frames for each user are different, the packet header ofeach of several frames may indicate the address of each user, the lengthof frame and/or unique frame data (e.g., {A1, L1, D1}, {A2, L2, D2} . .. ); and/or in an example case where the frames for each user areidentical, the packet header of each frame may indicate the address ofeach user, and common frame data (e.g., {A1, A2, Dcommon}).

FIG. 26 shows a message diagram for an example MU aggregation procedure2600 for short packets with OFDMA. The MU aggregation procedure 2600 maybe used to transmit short data packets to multiple users. In the exampleof FIG. 26, an AP may have a large amount of data 2604 ₁, 2604 ₂ and2604 ₃ to transmit to respective WTRUs 2601 ₁, 2601 ₂, and 2601 ₃. TheAP may have a small amount of data 2604 ₄, 2604 ₅ and 2604 ₆ to transmitto respective WTRUs 2601 ₄, 2601 ₅, and 2601 ₆.

The AP may set up a DL OFDMA transmission with the followingchannelization: WTRU 2601 ₁ on channel 2602 ₁; WTRU 2601 ₂ on channel2602 ₂; WTRU 2601 ₃ on channel 2602 ₃; and WTRUs 2601 ₄, 2601 ₅, and2601 ₆ on channel 2602 ₄. An OFDMA assignment frame 2630 (spanningchannels 2602 ₁ . . . 2602 ₄ and including OFDMA assignment frames 2603₁ . . . 2603 ₄) may be a control frame that may indicate thechannelization that is sent to the WTRUs 2601 ₁, 2601 ₂, and 2601 ₃ bythe AP. For example, WTRUs 2601 ₄, 2601 ₅, and 2601 ₆ may decode channel2602 ₄ with the MU aggregated frame 2604 ₇ to determine access theirdata.

The WTRUs 2601 ₁ . . . 2601 ₆ may receive respective data packets 2604 ₁. . . 2604 ₆. In an example, data transmissions 2604 ₁ . . . 2604 ₆ mayinclude dummy data and/or packet extensions so that all channels areoccupied equally for the duration of the transmission. On successfuldecoding of the respective packets 2604 ₁ . . . 2604 ₆, the WTRUs 2601 ₁. . . 2601 ₆ may send back respective UL ACKs 2606 ₁ . . . 2606 ₆. TheWTRUs 2601 ₄, 2601 ₅, and 2601 ₆ may send ACKs 2606 ₄, 2606 ₅, and 2606₆ in the order that the data is sent. The OFDMA assignment frame 2603 ₁. . . 2603 ₄ may set the time for transmission to cover all three ACKs2606 ₄, 2606 ₅, and 2606 ₆ so that other WTRUs 2601 ₄, 2601 ₅, and 2601₆ may set their network allocation vectors (NAVs) appropriately. Inanother example, the ACKs 2606 ₄, 2606 ₅, and 2606 ₆ may be sentsimultaneously, using for example an orthogonal code or sequence toenable separation.

FIG. 27 shows a message diagram for another example MU aggregationprocedure 2700 for short packets with OFDMA. FIG. 27 shows an identicalscenario to FIG. 26, and in addition the WTRUs 2701 ₁, 2701 ₂, and 2701₃ that do not transmit multi-user PPDUs may send multiple dummy ACKs2706 x to ensure that the channels 2702 ₁, 2702 ₂, and 2702 ₃ stayoccupied for the entire duration of the OFDMA TXOP.

FIG. 28 shows a message diagram for another example MU aggregationprocedure 2800. In the example of FIG. 28, the AP and/or the WTRUs 2801₁ . . . 2801 ₆ may have simultaneous transmit-receive (STR) capability(e.g., full-duplex radio or transceiver). FIG. 28 shows an identicalscenario to FIG. 26, however because of the STR capabilities, the ACKs2806 ₁ . . . 2806 ₆ may be sent immediately after the respective packettransmissions 2604 ₁ . . . 2604 ₆ are over. Additionally, ACK-End(ACK-e) frames 2806 _(E) may be sent at the end of the wholetransmission to indicate when the total OFDMA transmission is over.

In another example, MU ACKs may be aggregated to create a MU/A-MPDUBlock ACK or two dimensional (2D) block ACK.

Example procedures may be used to optimize the transmission of DL blockACKs when UL MU transmission occurs. Such example procedures mayinclude, but or not limited to, any of the following procedures. In anexample, the packet header may indicate that the block ACK is amultiple-WTRU block ACK. In another example, the packet header mayindicate the address of the recipient WTRUs. For example, a group ID mayindicate that addresses all the WTRUs in the UL MU transmission. Inanother example, a bit-map based on the positions of the WTRUs in the MUtransmission may identify the WTRUs that successfully transmit, suchthat WTRUs that transmit successfully may be set to 1 and vice versa;multiple receive addresses may be used. In another example, to limitoverhead, the block ACK may use a PAID or a group of PAIDs correspondingto the WTRUs to which the block ACK is being sent.

In another example, the packet header may indicate block ACK size toallow for acknowledgement of A-MPDU frames. For example, a separate sizemay be indicated for each WTRU. In another example, a variable sizebased on maximum A-MPDU may be transmitted by the WTRUs. In anotherexample, a fixed size based on maximum A-MPDU size specified instandard.

An example procedure to reduce the overhead of a DL block ACK inresponse to an UL MU transmission is described herein. In an example,WTRU1, WTRU2, WTRU3 and WTRU4 may transmit data to an AP in an uplink MUtransmission that may be UL-OFDMA or UL MU-MIMO. The AP may send anoptimized block ACK to the WTRUs. Procedures may be used in the casethat the information from certain WTRUs requires additional processingtime.

In this example, WTRU1 and WTRU2 may be successful, while WTRU3 andWTRU4 may need additional processing time. The AP may send asimultaneous ACK to WTRU1 and WTRU2. The AP may also send a simultaneousdelayed ACK transmission to WTRU3 and WTRU4. The ACKs may be transmittedat the same time. The AP may send a downlink OFDMA transmission toWTRU5, WTRU6, and WTRU7 on sub-channel 1, 2 and 3, for example in thenext or a subsequent transmission. The AP may send a multi-useraggregated ACK to WTRU3 and 4 at the same time on a sub-channel, forexample.

Example mechanisms and methods for MU aggregation for short packets withOFDMA may use a narrow center frequency. In an example, ACKs for eitherOFDMA or MU-MIMO transmissions on sub-channels may be sent on anassociated narrow center channel, sub-channel or resource unit (RU).

FIG. 29 shows a message diagram of an example MU aggregation procedure2900 for short packets with OFDMA and a narrow center channel 2901. Asin FIGS. 26-28, an AP may have a large amount of data 2904 ₁, 2904 ₂ and2904 ₃ to transmit to respective WTRUs 2601 ₁, 2601 ₂, and 2601 ₃. TheAP may have a small amount of data 2904 ₄, 2904 ₅ and 2904 ₆ to transmitto respective WTRUs 2901 ₄, 2901 ₅, and 2901 ₆. In the example of FIG.29, the center tones (e.g. center 26 tones) RU or sub-channel 2910 maybe used to send any of ACKs 2906 ₁ . . . 2906 ₆ and/or ACK-E 2906Eassociated with corresponding WTRUs 2901 ₁ . . . 2901 ₆ transmitted overchannels 2902 ₁ . . . 2902 ₄. This configuration may have the additionaladvantage that if there are no data packets to be sent, the centerchannel 2910 may still be used for the transmission of control packets(e.g., NDP's, or ACK's) without the need to modify the RF configurationfor the control packet transmissions.

In another example, the allocation of packets and their respective ACKsmay use a finer resource utilization than that shown in FIG. 29. FIG. 30shows a message diagram of another example MU aggregation procedure3000. In FIG. 30, resources for ten WTRUs 3001 ₁ . . . 3001 ₁₀ areaccommodated. In this example the individual channels 3002 ₁ . . . 3002₈ may utilize 26 tones for each WTRU 3001 ₁ . . . 3001 ₁₀ transmission3004 ₁ . . . 3004 ₁₀ and the associated ACKs 3006 ₁ . . . 3006 ₁₀ mayoccur on the center channel 3010, and/or on the WTRU's assignedsub-channel 3002 ₁ . . . 3002 ₈. The center channel 3010 may facilitateassignment to one or more WTRUs 3001 ₁ . . . 3001 ₁₀ for short packets,which may require lower BW transmissions (e.g., their associated ACKs inresponse to the opposite direction of the data transmission). MU-BAframe 3008 may serve as a multi-user block acknowledgment for WTRUs 3001₂, 3001 ₄, 3001 ₈, and 3001 ₉ and MU-BA frame 3012 may serve as amulti-user block acknowledgment for WTRUs 3001 ₁ and 3001 ₃.

Example procedures for bandwidth signaling using RTS and CTS may beextended to allow enhanced small data packet transmissions. In the samemanner that multiple duplicated RTS channels may be utilized forsubsequent duplicated packet transmissions, such procedures may beextended to allow multiple transmissions of small data packets whilemaintaining a low overhead.

An example procedure for bandwidth signaling using RTS and CTS forenhanced small data packet transmissions over two or more channels isdescribed herein. In an example, the channels may be 5 Mhz, 20 Mhz, oranother channel bandwidth. The procedure is may be referred to as anon-HT duplicate short data frame transmission procedure.

In an example, the AP may transmit a frame on the primary channel (e.g.,5 MHz or 20 MHz as in various IEEE 802.11 standards) for backwardscompatibility, and the short packet transmission may be allocated to thesecondary channels. In another example, instead of the AP transmitting aframe on the primary channel for backwards compatibility, the AP maysetup a non-HT duplicate frame allocation on the available channels(e.g., up to 80 MHz) for another short packet transmission.

In an example, multiple parallel short data packets may then be sent onmultiple parallel channels. The short data packets may have anindication in the MAC header or the SIG field for example, indicatingthat the short data packets are being sent using a non-HT duplicateshort data frame transmission. When a WTRU receives a non-HT duplicateshort data frame with the non-HT duplicate indication, the WTRU may knowto only send a single BA on the primary channel for all of the parallelreceived short data packets. In an example where all short data packetsare non A-MPDU, the single BA may be reused or re-interpreted for theaggregated short data packets from MU instead of single user. In anexample where one or more of the aggregated short data packets isA-MPDU, the single BA may be a two-dimensional BA as described above.

The example procedure for bandwidth signaling using RTS and CTS forenhanced small data packet transmissions may be extended to allow acombination of short and long data packets to be sent over multipleparallel channels. In an example, the AP may set up a non-HT duplicateframe allocation on the available channels (e.g., up to 80 MHz).Multiple parallel short data packets may be sent on multiple parallelchannels. The short data packets may have an indication in the MACheader or the SIG field for example, indicating that they are being sentusing a non-HT duplicate short data frame transmission.

In an example, a long data packet may be sent only on the primarychannel(s) by not including the non-HT duplicate short data frameindication in either the MAC header, or the SIG field. In an examplewhere a WTRU receives a non-HT duplicate short data frame with thenon-HT duplicate indication, the WTRU may only send a single BA on theprimary channel(s) for all of the parallel received short data packets,and another ACK or normal BA for the long data packet received on theprimary channel (s). In an example where all short data packets are nonA-MPDU, the single BA may be reused or re-interpreted for the aggregatedshort data packets from MU instead of single user. In an example whereone or more of the aggregated short data packets is A-MPDU, the singleBA may be two-dimensional BA as described above.

Although the approaches described herein may be described with respectto IEEE 802.11 protocols, they may be applicable to other wirelesssystems. Wherever a type of IFS is used, any other time interval may beused.

Although features and elements are described above in particularcombinations, one of ordinary skill in the art will appreciate that eachfeature or element can be used alone without the other features or inany combination with or without the other features and elements. Inaddition, the methods described herein may be implemented in a computerprogram, software, or firmware incorporated in a computer-readablemedium for execution by a computer or processor. Examples ofcomputer-readable media include electronic signals (transmitted overwired or wireless connections) and computer-readable storage media.Examples of computer-readable storage media include, but are not limitedto, a read only memory (ROM), a random access memory (RAM), a register,cache memory, semiconductor memory devices, magnetic media such asinternal hard disks and removable disks, magneto-optical media, andoptical media such as CD-ROM disks, and digital versatile disks (DVDs).A processor in association with software may be used to implement aradio frequency transceiver for use in a WTRU, UE, terminal, basestation, RNC, or any host computer.

What is claimed:
 1. A station (STA) configured for multi-user (MU)communications, the STA comprising: a receiver configured to receive acontrol frame, wherein the control frame includes uplink (UL) MUresponse scheduling information for transmission of a blockacknowledgement (BA) by the STA and BAs by a group of STAs; and atransmitter configured to transmit the BA, wherein the transmission ofthe BA occurs a SIFS interval after the received control frame as partof an MU transmission.
 2. The STA of claim 1, wherein: the receiver isfurther configured to receive a DL MU transmission, wherein the DL MUtransmission is one of a DL MU multi-input-multi-output (MIMO)transmission or a DL orthogonal frequency division multiple access(OFDMA) transmission.
 3. The STA of claim 1, wherein the control frameincludes at least one of the following information: a number of STAsscheduled to feedback an acknowledgment, an indication of the group ofSTAs scheduled to feedback an acknowledgment, a resource unit indicationfor each STA for the transmission of BAs, block acknowledgment request(BAR) control and BAR information for each scheduled STA, or anindication regarding permissible aggregation of BAs and other packets.4. The STA of claim 1, wherein: the receiver is further configured toreceive a data physical layer convergence protocol (PLCP) protocol dataunit (PPDU), wherein the BA acknowledges the data PPDU.
 5. The STA ofclaim 4, wherein the data PPDU is transmitted as part of a plurality ofdata PPDUs that are transmitted simultaneously over a plurality ofrespective resource units.
 6. A method, performed by a station (STA),for multi-user (MU) communications, the method comprising: receiving acontrol frame, wherein the control frame includes uplink (UL) MUresponse scheduling information for transmission of a blockacknowledgement (BA) by the STA and BAs by a group of STAs; andtransmitting a BA, wherein the transmission of the BA occurs a SIFSinterval after the received control frame as part of an MU transmission.7. The method of claim 6, further comprising: receiving a DL MUtransmission, wherein the DL MU transmission is one of a DL MUmulti-input-multi-output (MIMO) transmission or DL orthogonal frequencydivision multiple access (OFDMA) transmission.
 8. The method of claim 6,wherein the control frame includes at least one of the followinginformation: a number of STAs scheduled to feedback an acknowledgment,an indication of the group of STAs scheduled to feedback anacknowledgment, a resource unit indication for each STA for the feedbackof the BAs, block acknowledgment request (BAR) control and BARinformation for each scheduled STA, or an indication regardingpermissible aggregation of BAs and other packets.
 9. The method of claim6, further comprising: receiving a data physical layer convergenceprotocol (PLCP) protocol data unit (PPDU), wherein the BA acknowledgesthe data PPDU.
 10. The method of claim 9, wherein the data PPDU istransmitted as part of a plurality of data PPDUs that are transmittedsimultaneously over a plurality of respective resource units.
 11. Anaccess point (AP) configured for multi-user (MU) communications, the APcomprising: a transmitter configured to transmit a control frame,wherein the control frame includes uplink (UL) MU response schedulinginformation for transmission of a block acknowledgment (BA) by a groupof STAs; the transmitter further configured to transmit a data physicallayer convergence protocol (PLCP) protocol data unit (PPDU); and areceiver configured to receive the BA, wherein the BA is received atleast a short interframe spacing (SIFS) interval after the transmittedcontrol frame as part of an MU BA transmission, and wherein the BA isassociated with the data PPDU.
 12. The AP of claim 11, wherein thetransmitter is further configured to transmit a DL MU transmission,wherein the DL MU transmission is one of a DL MUmulti-input-multi-output (MIMO) transmission or a DL orthogonalfrequency division multiple access (OFDMA) transmission.
 13. The AP ofclaim 11, wherein the control frame further includes at least one of thefollowing information: a number of STAs scheduled to feedback anacknowledgment, an indication of the group of STAs scheduled to feedbackan acknowledgment, a resource unit indication for each STA for thetransmission of BAs, block acknowledgment request (BAR) information foreach scheduled STA, or an indication regarding permissible aggregationof BAs and other packets.
 14. The AP of claim 11, wherein the data PPDUis part of a plurality of data PPDUs that are transmitted simultaneouslyover the plurality of respective resource units.